1. Regarding ground of appeal No. 1

A. The Supreme Court's decision is that where both obligations are simultaneously performed in a bilateral contract, even if one of the parties' obligations becomes due, even if one of the parties' obligations becomes due, it does not assume liability for the delay of performance until the other party's obligation is performed, and such effect does not necessarily lead to the exercise of the right of defense for the simultaneous performance. Thus, where a party asserts that he/she is not liable for the delay of performance does not necessarily exercise the right of defense for the simultaneous performance. If the other party's obligation is provided in a bilateral contract which is simultaneously performed, if it is necessary to perform the other party's obligation, the preparation for the performance can be completed at any time, and the other party shall be notified and notified

B. (See, e.g., Supreme Court Decision 2001Da3764, Jul. 10, 2001).

For the reasons indicated in its holding, the lower court determined that, on the premise that the remaining obligation of the Defendant for the instant construction contract based on the instant construction contract and the obligation for the repair of defects against the Defendant for the Defendant for Jintopy Co., Ltd. are simultaneously performed, the Defendant’s simultaneous performance defense against the Defendant for the collection of the instant collection amount against the Defendant, which is the collection obligee, was accepted, and the Defendant, the third obligor, as the collection obligee, was paid KRW 10,165,320, and at the same time, the Defendant, as the collection obligee, was liable to pay the amount of KRW 4,858,450, which is within the scope of the remaining obligation for the Plaintiff, the collection obligee, as well as the amount of KRW 4,858,450, which is within the scope of the remaining obligation for the collection obligee, from the date following the date of delivery

C. However, in light of the legal principles as seen earlier, the Defendant’s remaining obligation for construction cost.