PURPOSE: To improve strength to horizontal force by fitting the lower end inner face parts of plural columns to a longitudinal wall provided along the vertical direction of a corridor floor frame disposed on the outside of a building, and fitting handrails to the outer face parts of the columns.

CONSTITUTION: A habitable room unit column 2 is erected at the angle part of a habitable room unit frame 1, and an exterior wall 3 is disposed around the frame 1 and the like. A corridor floor frame 12 of U-shape cross section is disposed on the outside of the frame 1, and the lower end inner face parts of columns 13 of lip channel shape cross section are fastened with bolts to the longitudinal wall 12a of the frame 12. Plural handrails 14 are then fitted to the outside of the columns 13 to form an outside corridor 11.