The judgment below is reversed and the case is remanded to Seoul High Court.

The grounds of appeal are examined (to the extent of supplement in case of supplemental appellate briefs not timely filed).

1. The lower court: (a) acknowledged that among the total project area of the instant case, the road 252,524 square meters was reverted to the Defendant free of charge; (b) the total site cost included only the expenses for the portion of the State-owned and public land, and did not calculate the site cost for the free reverted area; and (c) in calculating the site cost for the basic living facilities among the expenses for the installation of the basic living facilities included in the purchase price for the Plaintiffs, the said free reverted area should be excluded; and (d) calculated the site cost for the basic living facilities by means of seeking the ratio of the area for the installation of the basic living facilities, excluding the said free reverted portion, from

2. However, we cannot accept the fact-finding and decision of the court below for the following reasons.

Since the amount of unjust enrichment to be returned by the Defendant to the Plaintiffs is equivalent to the cost of the basic living facilities included in the sale price, the site cost of the basic living facilities, one of the constituent elements, shall be calculated by multiplying the total area of the land included in the total site cost, which is the basis for calculating the sale price, by the said total site cost in proportion to the area occupied by the basic living facilities.

However, according to the records, although the existing road 252,524 square meters has been gratuitously reverted to the defendant as the state-owned and public land, the defendant can be aware of the fact that the land which is gratuitously reverted is evaluated as 244,887,024,326 won and included in the site cost. Thus, the area of the gratuitously reverted portion should be included in the calculation of the site cost

Nevertheless, the court below's calculation of land costs for basic living facilities exceeds the limit of the principle of free evaluation of evidence against logical and empirical rules.