To attain low cost by improving an electric contact reliability as well as by reducing the number of parts.

A power-off device 1 consists of a housing 4, a plug 5 and a plug locking portion 8. When the plug 5 is inserted into an insertion slot 19 of the housing 4, an inserting direction edge 5c of the plug 5 abuts against a convex edge 8a of the plug locking portion 8 to once stop an inserting motion just before a power side terminal 10 and a load side terminal 11 short-circuit. The plug 5 is inserted into the housing 4 with high inserting speed to short- circuit both terminals 10 and 11 if a force beyond a predetermined insertion force is added to the plug 5. Since the inserting speed of the plug 5 is fast when an arc discharge is produced, the arc discharge is easily extinguished and the decrease of a contact reliability resulting from wear of the plug 5 and the like is reduced.