The Plaintiff is an enterprise that mainly engages in building and engineering work (the trade name before and after the change on April 14, 2017: C: hereinafter collectively referred to as “Plaintiff”), and the Defendant is an enterprise that mainly engages in manufacturing machinery and equipment and parts for civil and engineering work and wholesale and retail business.

On September 2, 2014, the Plaintiff concluded a construction contract (hereinafter “instant construction contract”) with the Defendant and the five parcels (hereinafter “instant factory site”) under which the Plaintiff was awarded a new construction contract for manufacturing oil-using machinery and equipment (hereinafter “instant factory”).

According to the instant construction contract, the construction period is four months after the conclusion of the contract, and the construction amount is KRW 2,167,00,000 (including value-added tax). 30% of the total construction amount is paid as the down payment on the date of conclusion of the instant construction contract, and the intermediate payment is paid according to the enhancement of the progress of the construction, and the remainder is paid within one month after the completion of the construction.

On December 28, 2014, the Plaintiff changed the construction amount under the instant construction contract into KRW 1,960,200,000 (including value-added tax) on the ground that the construction amount has been reduced due to a design change (unconstruction) with the Defendant.

During the construction process under the instant construction contract, the Plaintiff, upon the Defendant’s request, performed additional construction works, such as ① installation of a 65-meter radius on the floor of the first unit of the instant building among the six plant buildings, ② installation of a string string string string string string string string string string string string string string string string string string string string string string string string string string string string string string string string string string string string string string string string string string string string string string string st

The Plaintiff issued an electronic tax invoice amounting to KRW 2,030,600,000 to the Defendant regarding the construction project under the instant construction contract.