1. The part of the judgment of the court of first instance against the defendant shall be revoked.

2. The plaintiff's claim concerning the above cancellation part is dismissed.

1. The reasoning of this part of the judgment of the court is the same as the reasoning of the judgment of the court of first instance, and thus, this part of the reasoning is cited by the main sentence of Article 420 of the Civil Procedure Act.

2. Summary of the parties' arguments

A. The additional construction cost according to the price fluctuation of Plaintiff is also the construction cost corresponding to the contractor’s height. As such, the advance payment to be paid for additional construction cost of KRW 144,150,620 due to the price fluctuation in Pulung Construction should be appropriated for the amount of KRW 144,150,620.

Therefore, 150,619,630 won in the difference between the advance payment that the Plaintiff actually returned and the advance payment that should have been appropriated respectively to the existing construction cost and the above additional construction cost, i.e., the advance payment that the Plaintiff should have returned, i.e., KRW 76,41,415, and KRW 150 in the profits that the Defendant acquired without any legal cause, and thus, the Defendant should return it to the Plaintiff as unjust enrichment.

B. Defendant 1) cannot be deemed that advance payments guaranteed by the Plaintiff for the return are automatically appropriated for the additional construction cost due to price fluctuation. 2) It cannot be deemed that advance payments guaranteed by the Plaintiff for the return are appropriated for the construction cost that the Defendant directly pays to the subcontractor.

3. The advance payment that the Plaintiff guaranteed the return is paid by the Defendant as a part of the construction cost under the 6th construction contract, so the advance payment is limited to the construction cost corresponding to the 6th construction contract cost, and is not necessarily appropriated for the unpaid construction cost until the 1 to 5th construction work.

3. Determination

A. In order to ensure the smooth progress of construction without difficulty in the payment of materials security wages, advance payment of the relevant legal doctrine is not the prepaid construction cost that the contractor pays the construction cost to the contractor in advance, but the total construction cost paid in relation to the specific expiration of the construction cost.