To prevent a sub-connecting housing from moving out of a frame accidentally.

A frame 10 is mounted on a mounting hole 2 of a panel 1. A sub-housing 20 on a male side is inserted from a back side in a housing chamber 13 formed in the frame 10, and a protrusion 44 of a lock arm 43 provided on an outer surface of a back part side of the sub-housing 20 is elastically locked with a locking part 51 of a locking plate 50 provided on an inner surface of the housing chamber 13. An opposite female housing 30 engaged with the sub-housing 20 from a front side of the sub-housing 20 so that a large hood part 33 covers an outer periphery of a front end side of the sub-housing 20. A recessed part 37 is formed on a tip edge of the large hood part 33. When both of the housings 20, 30 are normally engaged, a tip of the lock arm 43 is inserted in the recessed part 37. As long as both of the housings 20, 30 are normally engaged, bend deformation of the lock arm 43 is restricted and a locking state to the locking part 51 is maintained.