On September 20, 2014, while constructing a building on the ground of Dongdaemun-gu Seoul, Dongdaemun-gu, Seoul, the Plaintiffs concluded a contract with E to lease KRW 1 billion, KRW 55 billion (including value-added tax, the last day of each month) of the lease deposit, and the term of lease from April 1, 2015 to March 31, 2020 (hereinafter “instant lease contract”).

B. After October 20, 2014, the Plaintiffs, E, and the Defendant concluded a lease succession agreement with the Defendant succeeding the status of the lessee from October 20, 2014 to the status of the said lease agreement.

C. Under the instant lease agreement, the agreement was concluded to handle the rent adjustment within the limit of the inflation rate in the previous year, which was disclosed from the Statistics Korea every year from the third year following the following.

Article 3 (Adjustment of Rental Deposit and Rent) The term of lease under this Agreement shall be five years, and the term of lease under this Agreement shall be the period of guarantee of goodwill (lease) for ten years.

The adjustment of rents shall be processed by mutual consultation within the limit of the inflation rate for the preceding year, which is disclosed by the Statistics Korea every year from the third year.

2. The parties' assertion

A. There is a variety of price index, such as the Plaintiff’s claim price index, producer price index, and export price index, and the phrase “within the limit of the inflation rate in the previous year which is disclosed by the Statistics Korea of every year” is unclear, and there is no binding force, and thus, the amount of rent increase as claimed in accordance with the claim for rent increase under Article 628 of the Civil Act is sought.

B. As stated in the instant lease agreement, which is the Defendant’s alleged disposal document, “within the limit of the inflation rate in the previous year that is disclosed by the Statistics Korea Statistical Office.”