To save a space, to simplify a structure of a top plate to realize a neatly clear-cut top place surface, to dispense with any tools in attaching/ detaching a lid for both inspection and heat radiation, and to facilitate the attachment/detachment work.

A monitoring and controlling appliance, a fan for heat radiation, etc., are stored in a box body 2, the lid 20 for both inspection and heat radiation is fitted to an opening 18 in the top plate 3 of the box body 2 by a locking tool 23 in a freely pressing, fitting, returning and detaching manner, and a wiring cap 14 for passing a cable 6 of the appliance on the top plate 3 is fitted to the lid 20. A finger is put into a cable passing port 22 of the cap 14, and the lid 20 is detached from the top plate 3 against the fitting force of the locking tool 23 by returning the finger.