To generate multiple house design plans approximate to optimum in short time by expressing the arranging position/arranging direction of a unit which is arranged at first in respective units constituting a building and the arranging order of the respective units constituting a building by genotyp information and executing genetic algorithm, based on a restriction condition such as the environmental conditions of the outline shape of a site and the life system condition of the number of rooms.

A design basic information input part 1 inputs basic information on the restriction condition of a house design, such as an environmental conditions and a life system conditions, request quality and weighting. A genotypic information generation part 2 is constituted of the respective elements of the arranging position and the arranging direction of the units, where genotypic information is arranged in the first building and the arranging order of the respective units. A gene with label, where the labels are added to individual information of the constitution, elements, is obtained and plural genetypic information on individuals are generated based on the restriction conditions. An expression-type conversion part 3 converts genetypic information of the respective individuals from the genetypic information generation part 2 into the quality evaluation index and the house shape of the house.