According to the reasoning of the judgment of the court below, the plaintiff and the defendant had already been leased to the non-party on this case. The plaintiff's obligation to return the remainder of the building, including the second floor of the building, was taken over by the plaintiff and agreed to settle the remainder by themselves without involvement in the contract as stated in its holding. The defendant had prepared documents necessary for the registration of transfer of the above real estate on March 31, 1978, and requested the plaintiff to postpone the payment of the remainder of the building by 7th day on which the plaintiff had not received the remainder of the building by 9th day, and the defendant had not received the remainder of the building by 7th day on which the contract had been rescinded. The plaintiff had not been notified that the remainder of the building had not been paid until 9th day on which the contract had been rescinded by 17th day on which the plaintiff had not been paid the remainder of the building by 4th day on which the plaintiff had not been notified that the remainder of the building had not been paid until 19th day.

The court below should have held that each of the obligations on the Bilateral Contract is simultaneously performed, in order to hold the other party liable for the non-performance of obligations, it is necessary to provide the other party with the performance of his own obligations and notify the other party of the performance of obligations. The sales contract on the real estate where the establishment of a neighboring mortgage is registered shall, barring any special circumstance, have the relationship between the seller's duty of registration of transfer of ownership and the buyer's duty of cancellation of the establishment of a neighboring mortgage (see, e.g., Supreme Court Decision 65Da1367, Sept. 7, 1965; 68Da2342, Jun. 5, 1973). The court below acknowledged that the establishment registration of a mortgage was completed prior to the original real estate at the time of sale and purchase, which was the object of which the plaintiff's obligation to pay for the non-performance of obligations. Thus, the court below should have established the above legal principles as to the seller's duty to pay for the non-party's own obligation to pay for the remainder of obligations.

Therefore, without having to undergo a judgment on the remaining grounds of appeal by the Plaintiff, the case shall be reversed, and the case shall be remanded to the Seoul High Court which is the original judgment, and it is so decided as per Disposition by the assent of all participating judges.

Justices Lee Il-young (Presiding Justice)