To maintain appearance quality and to maintain a mutual connection state even when external force acts without damaging articles to be taken in and out.

A back lower horizontal frame member 112A has a first beam part 122A2 projecting from a frame body 122A1, having a screw insertion hole 122A4, where a lower surface panel 121 is mounted on the upper surface. In the first beam part 122A2, the lower surface is above the lower surface of the frame body 122A1 and the height larger than the head part 16a of an attaching bolt 16 is secured between the upper surface thereof and the upper surface of the frame body 122A1. A connection bracket 30 has a pair of clamp piece parts 32 extended from both end parts of a base part 31 and a mounting piece part 33 extended in the form of following the lower surface of the first beam part 122A2 from the clamp piece parts 32. The attaching bolt 16 threadedly engaged to the female threaded hole 34 of the mounting piece part 33 through the first beam part 122A2, and the movement of the two back lower horizontal frame members 122A is regulated so as not to be separated from each other.