1. The Defendant (Counterclaim Plaintiff) paid KRW 109,186,080 to the Plaintiff (Counterclaim Defendant) and its related amount from March 21, 2013 to June 17, 2014.

A principal lawsuit and a counterclaim shall be deemed simultaneously.

1. Basic facts

A. The Plaintiff and the Defendant are both stock companies engaged in electrical construction business.

B. On August 6, 2012, the Defendant: (a) concluded a contract with Han-gu Co., Ltd. (hereinafter “Co.”) for the electrical construction and mooring works during the construction of facilities for the installation of facilities for the emission of sewage and wastewater in Seoul Metropolitan area (hereinafter “instant construction works”); (b) KRW 775,500,000 (excluding value-added tax; hereinafter the same shall apply) for the construction period from August 6, 2012 to June 26, 2013.

C. On August 8, 2012, the Plaintiff received a contract with the Defendant for the instant construction cost of KRW 425,700,000, and the construction period from August 6, 2012 to June 26, 2013.

(hereinafter referred to as the “instant contract”) between the Plaintiff and the Defendant.

According to Article 11 of the contract of this case, where there occurs an increase or decrease in construction volume due to the modification of the design, the parties may adjust the contract amount.

Meanwhile, according to Article 15(2) of the same contract, the construction cost shall be paid simultaneously with the delivery of the object of the construction project.

E. On March 2013, the Plaintiff suspended the instant construction work and transferred the construction site to the Defendant. By that time, KRW 133,769,381 was additionally required in the course of the Plaintiff’s implementation of additional construction without the instant contract due to design modification.

Meanwhile, the Plaintiff received KRW 330,500,000 from the Defendant as construction cost under the instant contract.

F. On May 28, 2013, the Defendant entered into a contract to modify the content that increases the construction cost of the instant construction in KRW 72,138,00 with respect to the instant construction work, thereby KRW 847,638,000.

[Ground of recognition] Facts without dispute, Gap 1 and 2 evidence, Eul 1 evidence (including each number; hereinafter the same shall apply), the appraiser Gap's appraisal result, the purport of the whole pleadings

2. The assertion and judgment

(a) the main office;