PURPOSE: To simplify the room layout design and improve the efficiency in designing.

CONSTITUTION: As for a building having a nearly rectangular plane on the first floor, an entrance part 2 is arranged on one edge part side of one side part of the first floor on the plane view, and each one part 3, 4 around a water device is arranged on the other edge part side, and each one part 5, 6 around the water device is arranged at the side part on the edge part side where each one part 3, 4 around the water device between both the side parts which are contiouous to the other side part. The residence parts 7, 8 and 9 such as living rooms 8 are arranged in an L shape on the plane view, along the rest two-side parts other than one side part and the side parts where the other parts 5 and 6 around the water device are arranged.