PURPOSE: To easily change the mode between the assembled state and folded state and allow mass production by forming a box body with a front plate section, the right and left side plate sections, a back plate section, and the openable upper and lower cover sections.

CONSTITUTION: For folding, cover sections 9, 10 are opened from the inside by a finger through a window hole, the cover sections 9, 10 are warped, a small triangular piece 14 is deployed, and a back plate section 11, the cover sections 9, 10, and the small triangular piece 14 are formed into a flat plate shape. The front plate section 6 of a front panel 3 is deformed into a flat plate shape, side sections 7, 8 are folded and overlapped on the front plate section 6 across side plate sections 12, 13, and a flat shape is formed as a whole. For assembling, the connection portions of the front panel 3 with the front plate section 6 and the side plate sections 7, 8 are fastened inward as shown by arrows. The angles between the front plate section 6 and the side plate sections 7, 8 are increased, the cover sections 9, 10 are pulled by the back plate section 11 and the small triangular piece 14 connected to the side plate sections 7, 8, and they are slid to the back face of the front plate section 6 curved into the protruded shape for natural assembling.