1. The Defendant’s KRW 262,672,792 as well as the Plaintiff’s annual rate of 6% from April 27, 2017 to May 7, 2020.

1. Basic facts

A. A. (1) The Plaintiff is a corporation established on February 16, 201 with the air-conditioning system’s wholesale, retail, and installation construction business’s business purpose; D’s representative director is a business of selling and installing air-conditioning equipment with the trade name “E”; however, on December 3, 2011, the Plaintiff entered into a contract with the Defendant to supply and install various auxiliary facilities (including construction cost 1,100,000,000 won (hereinafter “instant contract”) to the Jeju-si G Hospital (hereinafter “G Hospital”) newly constructed by the Defendant with the Defendant on December 3, 201 (hereinafter “instant contract”).

3) At the time of the instant contract, D and the Defendant specified the unit price for each item, such as interior equipment, outdoor equipment, heat exchange equipment, mutual conditioning equipment, pipes, etc., to be installed as the instant construction, and determined the construction cost of KRW 1,100,000 based on the detailed statement for each item, calculated by multiplying the volume, based on the method of adding up the unit price for each item, which is calculated by multiplying the volume by the unit price (Evidence A No. 4). D began the instant construction from March 2012 under the instant contract. As the design, etc. of the said new G Hospital was modified, D and the number of electric exchangeers, etc. to supply and install the said G Hospital increased.

5) Thereafter, D demanded the Defendant to modify the instant contract with the purport of increasing the price of KRW 1,320,00,000 on the ground of an increase in installation costs, such as a heat exchangeer added to a design modification, etc. However, the Defendant rejected it. 6) The Defendant: (a) on December 22, 2011; (b) KRW 40,000,000 on the account of the Nonghyup Bank; (c) KRW 40,000 on January 25, 2012; (d) KRW 40,000 on February 22, 2012; and (e) on the Plaintiff’s account of the Nonghyup Bank; (e) KRW 40,000,000 on March 22, 2012; and (e) KRW 40,400,000 on April 23, 201; and (e) KRW 30,000 on the basis of the Plaintiff’s account;