PURPOSE: To constitute a light-weight firm box body for a switchboard by installing a side plate, four sides of which are bent and to bent sections of which spacers are mounted, engaging and positioning the cylindrical projections of the spacers into engaging holes for a supporter fixed to a top plate and a bottom plate and fastening the top plate and the bottom plate to the side plate.

CONSTITUTION: The four sides of a sheet steel are bent at right angles to a main surface 1A and side faces 1B are formed, parts of the side face are bent inward and inner surfaces 1C parallel with the main surface are formed, and joint surfaces are fixed to each other through welding, etc. Each of the cylindrical projections 3A of spacers 3 set up to a side plate 1 is engaged with the engaging holes 6A of supporters 6 fitted to a top plate 5 and a bottom plate 6, and clamping bolts 7 are inserted from the bolt inserting holes 1E of the side plate, and clamped and fixed to the nuts 6B of the supporter of the ceiling plate and the supporter of the bottom plate, thus constructing a box body. Doors 8 are installed onto the front of the box body, and an instrument mounting frame is set up between the supporter of the top plate and the supporter of the bottom plate.