To efficiently convey component plate bodies as independent separate members and easily and quickly assemble the component plate bodies together in a single operation.

A connecting body is fixed to the junction section 11a of a side plate 1 by a set screw 58. There is a gap between the section 11a and the connecting body. When the insertion piece 22 of a back plate 2 is inserted into the gap between the connecting body and the section 11a while being guided by the guide side 57 of the connecting body, a groove section 22a is fit to a base section, the lower end of the insertion piece 22 is inserted into the gap while lifting an elastic arm 54 against the spring force of the elastic arm 54, and a lock hole 22b is coupled with a lock pawl 55 at the tip of the arm 54.