PURPOSE: To certainly detect that both housings are fit together perfectly.

CONSTITUTION: The first terminal 20 is projected on a vehicle side housing and the second terminal 23 is attached to a power side housing. The first contact part 24 on one end of the second terminal 23 touchably faces the first terminal 20 and the first opening and closing switch 29 of a detecting circuit 32 is formed between them. The second contact part 25 on the other end faces a contact point plate 27 stretched to the bottom face of a lock lever 10 and the second opening and closing switch 30 is formed between them. In a half fitting state as shown in C, the first opening and closing switch 29 is closed but the second opening and closing switch 30 is opened. Thereby, the detecting circuit 32 is not closed yet. When perfect fitting is achieved, the contact point plate 27 makes contact with the second contact part 25 of the second terminal 23 as a stopper 11 of the lock lever 10 is fit into a fitting aperture 18 as shown in D and the second opening and closing switch 30 is closed. Thereby, the detecting circuit 32 is closed.