1. The Defendant’s KRW 3,864,726,00 for the Plaintiffs and 6% per annum from May 28, 2019 to January 22, 2021.

1. Basic facts

A. 1) The Defendant’s Public Procurement Service published a public tender for D construction works that run across the interest districts and the wife population in Young-si (hereinafter “instant construction works”) around 2007.

2) The Plaintiffs organized a joint supply and demand body (share ratio: Plaintiff A: 80%, Plaintiff B Co., Ltd., 10%, Plaintiff C Co., Ltd., 10%, and hereinafter “instant joint demand body”) with the representative company of Plaintiff A Co., Ltd. (hereinafter “Plaintiff A”), and participated in the bid and decided as successful bidders. On March 21, 2008, the Plaintiffs entered into the contract agreement with the Defendant (the head of the Public Procurement Service) with the Seoul Regional Land Management Office as the contract amount of KRW 50 million, the contract amount of the instant construction work, the date of its commencement, March 26, 2008; June 24, 2008; the date of its completion; and the construction period from the commencement date to the commencement date of construction to the date of completion; each of the total construction period; and each of the construction works is determined as the completion date of construction works; and each of the construction works is determined as the completion date of construction works (hereinafter “construction works”).

3) Of the general terms and conditions of the construction contract included in the instant contract (hereinafter “instant general terms”) related to the instant case are as follows.

Article 20 (Adjustment of Contract Price due to Modification of Design) (1) Where there occurs an increase or decrease in construction volume, such as a change of construction methods for modification of design, or change of input materials, a public official in charge of a contract shall adjust the contract amount according to the following standards:

1. The unit price for the increased or decreased volume of construction works shall be the unit price per contract;

(B)

2. Items or cost items that are not written calculation details (including where the performance, standard, etc. is different even for the same item);

The unit price for a new item (hereinafter referred to as "new item") at the time of design modification (where the design is to be modified, when the agency awarding the contract has determined the modified plan, and where the design is not required to be modified, the modification shall be made between the parties to the contract in writing.