1. The part against the defendant among the judgment of the court of first instance is revoked, and the plaintiffs' claim corresponding to the revoked part is revoked.

1. The court's explanation on this part of the basic facts is identical to the corresponding part of the judgment of the court of first instance, and thus cite it as it is by the main text of Article 420 of the Civil Procedure Act.

2. The plaintiffs asserted that in calculating the sale price (sale conversion price) under each of the above parcelling-out contracts concluded between the plaintiffs and the defendant, since the housing site offered to the apartment of this case is public housing site, the Housing Site Development Business Guidelines, which is a legal order, applies to the housing site development business guidelines, and therefore, the housing site cost should be calculated at 70% of the cost of the housing site development in accordance with the above guidelines, the defendant applied 100% to the defendant, and the plaintiffs paid all the sale price stated in the "sale price" column in the attached Table 2 of the above mentioned above to the defendant. Since the part of the above parcelling-out contract exceeds the legitimate pre-sale conversion price due to erroneous calculation of the housing site cost as above is invalid in violation of the mandatory law, the defendant gains profits equivalent to the above money

Therefore, the defendant asserts that the plaintiffs have a duty to return the amount of money equivalent to the stated in the column of "the purchase price" as unjust enrichment from each of the stated amounts in the separate sheet of attached Form 2 "the amount calculated by deducting the amount stated in the column of "the legitimate conversion price".

3. Determination

A. According to Article 21(1) and (10) of the former Rental Housing Act (Amended by Act No. 10463, Mar. 9, 201); Article 23(8) of the former Enforcement Decree of the Rental Housing Act (Amended by Presidential Decree No. 22689, Mar. 2, 201); Article 14 and Article 9(1) [Attachment 1] of the former Enforcement Rule of the Rental Housing Act (Amended by Ordinance of the Ministry of Land, Transport and Maritime Affairs No. 350, Apr. 11, 2011), where a rental house is converted for sale, the pre-sale conversion price shall be calculated by calculating the arithmetic average of the construction cost and the appraised value. In such cases, the construction cost shall be the housing value at the time of the first tenant recruitment, which is the sum of the construction cost and the construction cost.