A. The Plaintiff is a company that operates the Integrative Construction, etc., and the Intervenor joining the Defendant is a regional housing association established to carry out the Gurisi Si E-si Apartment Construction Project (hereinafter each of the instant apartment buildings and the instant project), and the Defendant B Co., Ltd. (hereinafter the “Defendant Company”) is the Defendant’s agent for the instant project, and the Defendant C is the representative director of the Defendant Company.

B. On October 2014, the Plaintiff, the Intervenor, and the Defendant Company entered into a contract with the ordering person, the Defendant Company’s agent, and the Plaintiff, with respect to the remodeling construction work of the apartment model house (hereinafter “instant construction work”) from October 1, 2014 to November 15, 2014, with respect to the construction work period of the instant apartment model house (hereinafter “instant construction work”).

C. After November 2, 2014, the Plaintiff, the Intervenor, and the Defendant Company concluded a contract with the effect that the construction cost of the instant construction works increases by KRW 26,300,000 (excluding value-added tax) for the instant construction works, and concluded that the construction cost of the instant construction works was KRW 685,300,000 (=659,000,000 KRW 26,30,000).

(hereinafter referred to as the “instant contract” in combination with each of the above contracts.

On November 13, 2014, the Plaintiff completed the instant construction work.

E. Of the instant construction cost, only KRW 220,00,000, totaling KRW 72,490,000 on October 22, 2014, and KRW 147,510,000 on October 28, 2014, only KRW 220,000,000 was paid to the Plaintiff via Korea Asset Trust Co., Ltd. (hereinafter “Korea Asset Trust”).

바. 이에 원고는 2014. 12.경부터 피고 회사 및 피고 C에게 수회 미지급 공사대금의 지급을 요청하였는데, 이에 따라 피고 C은 2015. 2. 5. ‘원고 대표이사 귀중. D조합주택 인테리어 공사대금 壹億을 2015. 2. 6. 지급할 것을 각서합니다. 2015. 2. 5. C’이라는 내용의 지불각서 갑 제3호증, 이하 '이 사건...