To prevent first, second connector housings from being left in a half-engaged state.

First and second connector housings 11, 41 are made into a normal engaged state by a screw engagement of a bolt member 80 attached to the second connector housing 41 into a nut member 12 attached to the first connector housing 11. When the first and second connector housings 11, 41 are in the normal engaged state, an engaging part 99 of a cap 90 engages an engaged part 65 of the second connector housing 41, and when the first and second connector housings 11, 41 are not in the normal engaged state, the engaging part 99 does not reach a position for engaging the engaged part 65 in a state in which a contact part 94 of the cap 90 is in contact with a contacted part 84 of a head 81.