PURPOSE: To obtain excellent building constructional strength, reduce a construction cost, and use an indoor space effectively.

CONSTITUTION: A pair of left/right bearing walls 3 are arranged at an interval H. Respectively opposed rigid frame column parts 4 having a cross section being long in the ridge direction are formed at regular intervals in a span P on the inner surface sides of these left/right bearing walls 3. The upper parts of these paired left/right rigid frame column parts 4 are connected to each other by means of span directional lateral rigid frame beam members 5. The upper parts of the rigid frame column parts are also connected to each other along the upper parts of the bearing walls 3 by means of longitudinal rigid frame beam members 7. The floor surface is formed integrally with both the beam members 5 and 7. Thereby, since the front and the rear of a building can be opened extensively, an indoor space can be secured efficiently between the bearing walls 3, so that construction cost can be also reduced.