PURPOSE: To save energy for form assembly work by connecting continuously a plurality of the same shaped PC plates as that of columns and beams to provide confronting inclined planes and hinge shaped metal fittings to side alignment faces of every PC plate.

CONSTITUTION: The same shape thin flat plate concrete 1a - 1d as that of outsides (a) - (d) of columns, beams A and others are placed on a standard foundation. After that, inclined planes P having an inclination of about 45 degrees against the standard foundation are provided to every alignment side and, at the seame time, hinge shaped metal fittings 2 are fixed to every inclined plane P. Then, cotters 5 to make bond with later place concrete better are provided. After hardening the concrete, demoldings are made to bring the concrete to a site, and the hinge shaped metal fittings 2 are swivelled to confront the inclined planes P and to assemble the concrete. In addition, bar arrangement is made to the inside of a hollow section, and concrete is placed. According to the constitution, various dimensions and shapes of forms can be safely and easily assembled at a low cost.