Among them, the part against the Defendant (Counterclaim Plaintiff) and the part against the counterclaim are reversed, and this part of the case is reversed.

1. With respect to the Plaintiff (Counterclaim Defendant; hereinafter “Plaintiff”)’s appeal, the Plaintiff (Counterclaim Defendant; hereinafter “Plaintiff”) did not submit the grounds of appeal within the lawful period of submission.

2. As to the Defendant-Counterclaim Plaintiff’s ground of appeal

A. According to the reasoning of the judgment below, in full view of the adopted evidence, the court below held that the Defendant (Counterclaim Plaintiff; hereinafter “Defendant”) who received a contract from the council of occupants’ representatives in Gangdong-gu, Seoul, for the installation of CCTV (hereinafter “instant construction”) was obligated to pay KRW 296,635,00 of the cost of civil engineering works for underground CCTV for the purpose of the construction of omitted CCTV pipelines, even though it is essential for the execution of the instant construction works in subcontracting the Plaintiff, and on the other hand, the Plaintiff was obligated to pay KRW 616,910,00 of the cost of construction works paid by the Defendant and KRW 469,442,294, the difference between KRW 147,467,706 and KRW 147,467,700 of the cost of the instant construction works, and thus, the additional construction cost that the Defendant would ultimately be deducted from the Plaintiff’s payment to the Plaintiff by the Defendant.

However, in the process of calculating the above amount, the lower court calculated the cost of the engineering work for laying CCTV pipes underground on the basis of the appraisal result of appraiser D of the lower court based on the Plaintiff’s application (hereinafter “the result of the first appraisal”), and calculated the cost of the CCTV pipeline construction among the cost of the installation of CCTV pipes based on the measurement result of appraiser D of the lower court based on the Defendant’s application by the Defendant (hereinafter “the result of the second appraisal”) under the premise that the cost of the materials per mar of the instant PE30 pipelines was KRW 28,484, and the cost of the installation of CCTV pipes based on the mar of the instant PE50 pipelines was KRW 900.

B. However, it is difficult to accept the above measures by the court below for the following reasons.

(1) The record reveals ① The calculation of the construction cost under the instant construction contract.