To simplify the construction at a construction field, and to form a flat floor without generating a stage difference between a floor of a building frame side and a floor of a cubic in the construction of cubic.

A cubic 1 is formed of assembled walls 2 and a ceiling fitted to a space between upper parts of the walls 2, and an opening as an entrance 21 is formed in one of the walls. Sanitary equipments 10, 17 are assembled into the cubic 1, and the opening part is opened at a lower part thereof, and the lower opening part is reinforced by a separate member, and a height adjusting mechanism is fitted to a lower part of a petitioning wall 4 for partitioning inside of the cubic 1.