PURPOSE: To dispense with fixing members, such as screws in order to facilitate inspection, maintenance, cleaning, etc., by forming detaining borders at the ends of the bottom plate of a main frame, and detaining side covers and a rear cover.

CONSTITUTION: The main frame 2 of a main copying machine 1 has a bottom plate 3 having detaining borders 3a at parts of the bottom. The detaining border 5a of the lower part of each side cover 5 is detained with the detaining border 3a from the inside, and the upper border of the cover 5 curves on the side of the frame 2. The end of the detaining border 6a at the lower border of a rear cover 6 is provided with a fitting groove 6b for fitting the border 3a, and the upper border of the rear cover 6 curves likewise, and fitted to the fitting groove 8a of a cover 8.