The part of the judgment below's claim for restitution of unjust enrichment is reversed, and this part of the case is remanded to the Incheon District Court.

The grounds of appeal are examined.

1. As to the ground of appeal by the Plaintiff (Counterclaim Defendant; hereinafter “Plaintiff”)

A. As to the grounds of appeal related to the part on the claim for restitution of unjust enrichment in the principal lawsuit, where a contract contains a provision on the claim for restitution of unjust enrichment, it may be meaningful as a matter of principle or a variety of grounds, such as reserving the right to statutory rescission. Even in cases where the right to rescission is reserved, there are cases where a party intends to decide on the grounds of special cancellation in consideration of the purpose of the contract, etc., and allow the party to cancel the contract without a reasonable time limit. Whether a provision on the right to rescission is established with a certain intent shall be reasonably interpreted in accordance with logical and empirical rules, taking into account the purpose of the contract, circumstances under which the right to rescission is established, and the language and text of the clause itself, etc., as a matter of interpretation of intention, the other party to the contract, as well as the special grounds for cancellation, clearly stating that the other party may cancel the contract if one of the parties is not liable to both parties, and if there are circumstances such as only a certain party’s non-performance related to the performance of obligation, or a cause for which the right to cancel is not included, it is necessary to determine the real intent of the contract.