A. The Plaintiff received a payment of KRW 1,880,00,000 for the construction work of machinery among the construction works “B” from the Defendant, and subsequently, the Plaintiff decided to change the construction cost to KRW 1,801,865,00 due to the change in the design of the construction work, and the Plaintiff completed all of them.

In order to pay the price in installments, the defendant prepared a contract by dividing the construction cost into KRW 1,385,50,000 and KRW 416,365,00, and requested the issuance of a tax invoice and payment procedure.

Accordingly, the plaintiff and the defendant newly prepared a contract to change the construction cost into KRW 1,385,50,000, and the defendant paid all of KRW 1,385,50,000 to the plaintiff.

However, with respect to the remaining KRW 416,365,00, the defendant did not prepare a written contract and paid KRW 178,365,000 among them, and did not make a written contract for KRW 238,00,000.

Therefore, the Defendant is obligated to pay the Plaintiff the unpaid construction cost of KRW 238,000,000 and delay damages.

B. Defendant 1) According to the design change, the changed construction cost is KRW 1,385,50,000. (2) The Plaintiff agreed to undertake an additional construction work for the installation of the said machinery, other than the installation of the machinery, during the construction work of “B”. Around February 2015, the Plaintiff unilaterally suspended construction work after completion of only the excess work equivalent to KRW 178,365,000 of the supply value corresponding to the first portion of the said machinery.

Accordingly, the Defendant paid to the Plaintiff KRW 178,365,00 as the payment for completed portion, and the remainder of the additional construction work was completed on or around April 2015, and thus, there is no obligation to pay the remainder of the additional construction cost in addition to KRW 178,365,00 corresponding to the portion performed by the Plaintiff.

C. The key issue is that the claim is part of the original construction cost whose claim is modified, and the defendant asserts that it is the cost of the supplementary construction work for Drain. Accordingly, the defendant below.