1. The plaintiff (Counterclaim defendant)'s appeal against the principal lawsuit is dismissed.

2. The part concerning the counterclaim among the judgment of the court of first instance is relevant.

The principal lawsuit and counterclaim shall be judged together.

1. Basic facts

A. On March 21, 2014, the Defendant entered into a contract for construction works with the Plaintiff, each of which contracts was made for construction works for the construction of a villa on the ground (hereinafter “the construction works for the construction of a villa”) and construction works for the extension of the main pipe on the ground outside the F in Jinju-si and four parcels (hereinafter “the construction works for the extension of the main pipe”) on June 25, 2014.

B. The Plaintiff completed the construction on March 31, 2015, which is the date of completion, and obtained approval for the use thereof. As to the extension construction in this Sub-section, the agreement between the Plaintiff and the Defendant on the increase and decrease of the construction cost and the change in design, etc. after the conclusion of the said contract was not reached. Ultimately, the Plaintiff continued the said construction on January 2015, and the Defendant directly ordered the electrical construction and the external board construction among the extension construction in this Sub-section.

C. After September 21, 2015, the Plaintiff notified the Defendant of the cancellation of the main construction contract, and the Defendant also notified the Plaintiff of the cancellation of the said contract, and the said contract was rescinded at that time.

The Defendant paid the Plaintiff the total of KRW 4,051,031,485 for the construction cost, and KRW 2,760,000,000 for the extension of the main office to the Plaintiff ( KRW 1,291,031,485 + KRW 2,760,00,000).

[Reasons for Recognition] Unsatisfy, Gap evidence 1, 2, and 4 (including each number in the case of additional number), Eul evidence 7, the testimony of the witness of the first instance court H, the purport of the whole pleadings

2. The parties' assertion

A. A. The summary of the Plaintiff’s assertion 1) The construction cost of a new construction project is KRW 1,745,300,00 as stated in the contract, and accordingly, the Defendant received only KRW 1,291,031,485 out of the said construction cost, and the Defendant received only KRW 454,268,515 (=1,745,300,000 - 1,291,031,485) from the Plaintiff. Therefore, the Defendant is obligated to pay the remainder of the construction cost to the Plaintiff.

With respect to the construction cost of a new construction project.