(b) Where several sales contracts are null and void, the nature of a claim for return of unjust enrichment equivalent to the down payment;

(c) Whether the purchaser of the sales contract who has not obtained permission for transaction under the Act on the Utilization and Management of the National Territory can claim the return of the down

(d) Where a sales contract for a state of flexible invalidation without obtaining permission for the Act on the Utilization and Management of the National Territory becomes conclusive;

B. In cases where a creditor or debtor is a number of persons, each creditor or debtor has a right and bears an obligation in equal ratio, unless there is any special declaration of intention. Therefore, in cases where the seller of four persons, including the defendant, entered into a contract to sell forest to four persons, including the plaintiff, the claim for the return of the down payment as unjust enrichment on the ground of invalidation of the sales contract cannot be an indivisible obligation relationship, barring any special circumstances, and thus, the defendant, only one of the buyers, cannot be deemed to have a duty to return the down payment to the plaintiff, which is only one of the

C. The sales contract, which was concluded before obtaining permission from the competent Do Governor for the land within the regulatory zone under the Act on the Utilization and Management of the National Territory, is null and void since it is a contract that excludes or destroys the above permission from the beginning, but is based on the premise that permission is not granted, it does not differ from the case of conclusive invalidation as to the transfer of ownership, etc. as a juristic act with complete legal acts until the permission is granted. However, once the permission is granted, the contract becomes effective retroactively, and becomes null and void if the permission is granted otherwise, the contract becomes null and void, so it shall be deemed that there is a dynamic invalidation status until the permission is granted. The parties who concluded the contract with the dynamic invalidation status shall have a duty to cooperate with each other so that the contract can be completed with both parties. As such, the parties who concluded the contract with the dynamic invalidation status, which is not the provision excluding or avoiding the permission, cannot seek the return of the contract with unjust enrichment unless the contract becomes null and void in a state of dynamic invalidation, and can seek the return of the contract.

D. A contract on the state of flexible invalidation without permission for a transaction under the Act on the Utilization and Management of the National Territory shall be null and void on a conclusive basis, not only when there is a non-permission disposition by the competent Do governor, but also when both parties clearly express their intent not to file an application for permission.

On the first ground for appeal

(1) According to Article 21-3(1) and (2) of the Act on the Utilization and Management of the National Territory, where a contract for land, etc. is to be entered into within a regulatory zone designated pursuant to Article 21-2(1) of the same Act, the permission of the competent Do Governor shall be obtained. However, with respect to a contract for land, etc., the area of which does not exceed the area for each use as determined by the Presidential Decree, comprehensively taking into account the general economy and land price trends, transaction unit size, etc., the report shall be made to the head of the competent Si/Gun/Gu after entering into the contract. Article 21-3(8) of the same Act delegates matters necessary for calculating the area of the land. Accordingly, Article 25(3) of the Enforcement Decree of the same Act provides that “where a contract for land, etc. is entered into with a person again within one year after entering into a contract for land use for a group of persons, all or part of the remaining land, etc. shall be deemed a transaction for the whole land.”

(2) In light of the above purport of the Act and subordinate statutes, when the same party intends to enter into a sale contract on the land of several lots within the regulatory zone under the Act on the Utilization and Management of the National Territory, the transaction unit area that simply distinguishs the transaction subject to permission or the transaction unit area that simply distinguishs the transaction subject to permission shall not be determined by parcel according to the area of each parcel, but shall be determined on the basis of the total area of several lots of land in a case where the whole parcel of land appears to be the object of a sale contract by comprehensively taking into account the geographical closeness and utilization of the purpose of the land, economic purpose of the transaction concerned, and method of determining the price, and even if the buyer or seller is a number of persons, the above transaction unit area shall not be determined on the basis

(3) According to the records, the instant forest area was designated as a regulatory zone under the Act on the Utilization and Management of the National Territory by the public notice of the construction division, and the area of the instant forest area was more than 6,000 square meters, and the instant two lots of forest land were concluded as a single contract and the sales contract was determined in a lump sum without distinction of the relevant land. Therefore, the transaction unit area of the instant sales contract should be deemed as the total area of the instant two lots of forest land, and even if the buyer and seller respectively are four and the area of the said land does not amount to 6,00 square meters, so long as the total area of the instant two lots of forest land, which is the transaction unit, exceeds 6,000 square meters, the instant sales contract shall be deemed as a transaction subject to permission under the Act on the Management and Utilization of the National Territory, regardless of the size of land or the number of transaction parties.

The judgment of the court below to the above purport is justifiable, and there is no error of law by misapprehending the legal principles on land transaction permission under the Act on the Utilization and Management of the National Territory such as theories.

There is no reason to discuss this issue.

On the second ground for appeal

(1) In the event that a number of creditors or debtors are multiple persons, each creditor or debtor has a right and has an obligation in equal ratio, unless there is any special declaration of intention, and even though the seller of four persons including the defendant, concluded a contract to sell the forest of this case to four buyers including the plaintiff, the court below held that, with respect to the plaintiff's conjunctive claim seeking the return of the down payment of this case as unjust enrichment on the ground of invalidation of the sales contract of this case, the defendant, only one of the buyers, has an indivisible obligation to return the down payment to the plaintiff, who is only one of the buyers, without any instruction as to what special circumstances the claim was indivisible obligation. Thus, the court below erred in the misapprehension of legal principles as to the obligation and obligation between the majority parties, which affected the conclusion of the judgment.

(2) However, the court below determined that the sales contract of this case was a transaction subject to permission under the Act on the Utilization and Management of the National Territory without obtaining permission, and determined that the contract is null and void a year, and that the seller is liable to return the amount received as a down payment to the defendant as the seller in unjust

However, a contract concluded before obtaining permission from the competent Do Governor for the land within the regulatory zone under the Act on the Utilization and Management of the National Territory is null and void in terms of the terms of the contract that excludes the above permission from the beginning, but it is not likely to be effective in terms of the terms of the contract that is premised on obtaining permission (a contract that is not a contract for the extension of permission or locked contents shall be deemed to fall under this case). Although the above conclusive invalidation is not different from the case of a contract that is a complete juristic act under the Act until permission is granted, the contract shall be deemed null and void in terms of its retroactive validity, and if permission is granted, it shall be deemed that the contract becomes null and void in terms of its final and void, and it shall be deemed that there is a duty to cooperate with one another to ensure that the contract is completed by both parties, and thus, the contract shall not be deemed null and void in terms of the circumstances where the seller voluntarily concludes the contract for the return of unjust enrichment to the Do Governor (see Supreme Court en banc Decision 90Da1243, Dec. 24, 1991).

According to the records, this case's sales contract for the forest land of this case in the regulatory zone cannot be seen as excluding permission from the competent Do Governor or avoiding permission. Therefore, the above sales contract is a contract for the state of flexible invalidation. Therefore, the court below should order to return the down payment received by the seller as unjust enrichment only in cases where it becomes final and conclusive invalid after examining whether the state of flexible invalidation is finally null and void.

Therefore, without examining the remaining grounds of appeal, the part concerning the conjunctive claim among the judgment below is reversed, and the case is remanded to the court below. It is so decided as per Disposition by the assent of all participating Justices.

Justices Song Man-man (Presiding Justice)