To decrease man-hour for assembling and to improve strength and rigidity by a method wherein a left side plate and a right side plate are connected with a bottom plate through hinges and a back plate is fitted on the bottom plate and the left and right side plates and the front end faces of the left and right side plates and a front plate are slidably fitted by a hooking structure.

Left and right side plates 4 and 5 are respectively connected with a bottom plate 3 through hinges 11 being thinned by compression and a back plate 6 is also connected with the back plate through a similar hinge. In addition, on the front end faces of the left and right side plates 4 and 5, projected lines 15 for hooking are provided and recessed lines 16 for hooking are provided on the back face of a front plate 7 and the recessed lines 16 for hooking are slidably fitted and fixed to the projected lines 15 for hooking in the upward direction from the bottom. At the same time, the front end face of the bottom plate 3 is run on a small projection 17 on the back face of the front plate and is positioned between the upper small projection 17 and a lower stopper projection 18 to constitute a drawer. As slide fitting is performed like this way from the bottom to the top, even when a handle 10 of the front plate 7 is operated from the bottom in the upward direction, it makes the fitting condition more strong.