1. The plaintiff (appointed party)'s appeal is dismissed.

2. The costs of appeal shall be borne by the Plaintiff (Appointed Party).

1. The reasoning for the court’s explanation on this part of the basic facts is that the “basic facts” under Article 420 of the Civil Procedure Act is the same as the stated in the reasoning of the judgment of the court of first instance.

2. Determination on the cause of the claim

A. The gist of the Plaintiff’s assertion is that the pre-sale conversion price of the instant apartment is “the arithmetic mean of the construction cost and the appraised value” under the relevant laws and regulations, but it does not exceed “the amount obtained by deducting the depreciation cost during the rental period from the housing price calculated at the time of conversion into sale based on the construction cost of rental housing and housing site cost.” Meanwhile, the construction cost reflected in the above construction cost is not the standard construction cost but the construction cost actually invested

However, the sale price that the plaintiff and the designated parties paid to the defendant exceeds the legitimate conversion price calculated based on the construction cost actually invested in the apartment of this case. Since the excess is null and void in violation of the mandatory law, the defendant shall return the excess amount to the plaintiff and the designated parties as unjust enrichment.

B. (1) Determination of relevant legal principles (A) The pre-sale conversion price for publicly constructed rental housing, the mandatory rental period of which is five years as in the instant apartment house, shall be calculated by calculating the arithmetic mean of the construction cost and the appraised value, and the said price shall not exceed the amount calculated by subtracting the depreciation costs during the rental period from the housing price (calculated price) calculated at the time of conversion for sale based on the construction cost and housing site cost of the relevant rental housing pursuant to the former Enforcement Rule of the Rental Housing Act.

(B) Relevant statutes, such as the Rental Housing Act, with regard to the standards for calculating pre-sale conversion conversion price, including the Rental Housing Act, are aimed at facilitating the construction of rental houses and ensuring the stability of national housing life. To achieve its purpose, the Rental Business operator is also a rental business operator.