To prevent a key plate from impairing a main body, by a constitution wherein the operation of the key plate is prevented by an engaging plate even when locking is made by a key when a drawer is opened.

When the drawer is held in the main body, a button 7 of the engaging plate 10 comes into contact with a stile 12 of the main body and the button 7 gets inside a little, compressing a spring 8. The other side of the engaging plate 10 is formed in the shape of a letter U or reverse L, and when locking is made by a lock 5, the button moves enough to engage with the engaging plate 10 and gets into the U-shaped or reverse-L-shaped part of the plate 10 to be locked. When the drawer is pulled out, the button 7 detaches from the stile of the main body, moves by the dimension of a gap between a fitting plate and the engaging plate 10 formed when the drawer is held, comes into contact with the fitting plate and stops. Even when locking is attempted in this state, it cannot be executed.