1. The judgment of the court of first instance is modified as follows.

The defendant shall pay to the plaintiff KRW 3,911,00 on May 29, 2018.

1. Basic facts

A. On September 22, 2017, the Plaintiff concluded a construction contract (hereinafter “instant construction contract”) with the Defendant setting the construction cost of KRW 103,000,000, and the construction period of KRW 103,000 from September 23, 2017 to December 30, 2017, the submission of a letter of performance guarantee of defects (one year of defect warranty liability), and the submission of a letter of performance guarantee of defects (one year of defect warranty liability), and the construction contract (hereinafter “instant construction contract”).

B. The Plaintiff completed the instant construction, and the detached house newly built by the instant construction (hereinafter “instant building”) obtained approval for use on January 29, 2018.

C. From September 22, 2017 to January 30, 2018, the Plaintiff received KRW 98,800,000 from the Defendant as the instant construction price.

[Ground of recognition] Facts without dispute, Gap 2-4 evidence, Eul 1-2 evidence, the purport of the whole pleadings

2. The assertion and judgment

A. The Plaintiff’s assertion 1) The construction cost of this case is KRW 103,00,00, and the construction cost paid by the Defendant to the Plaintiff is KRW 98,80,000,00, and the Defendant is obligated to pay the Plaintiff the unpaid construction cost of KRW 4,20,000. 2) The Plaintiff, upon the Defendant’s request, performs additional construction works of internal embankments, small-scale kitchen, living room building distribution work, building building installation work, front balcony of the building, and front and rear balcony of the building. Thus, the Defendant is obligated to pay the Plaintiff additional construction cost of KRW 12,271,820.

B. According to the above facts of determination as to the claim for the unpaid construction payment, the Plaintiff completed the instant building under the instant construction contract. Thus, the Defendant is obligated to pay the Plaintiff KRW 4,200,000 (= KRW 103,000,000 - 98,800,000), barring any special circumstance, deducting the construction payment already paid from the agreed construction payment. 2) The Plaintiff and the Defendant’s assertion for the deduction of liquidated damages at the rate of KRW 1/100 per day between the Plaintiff and the Defendant.