To detect the engaging state of both housings with an electric wire cover.

When female and male housings 10, 40 are engaged while covering the electric wire cover 60 on the back end face 10A of the female housing 10, the electric wire cover 60 cannot be mounted on the male housing 40 since the locking part 61 of the electric wire cover 60 is disposed at the position separate from the part 49 to be locked of the male housing 40 until both the housings 10 and 40 arrive at a regular engaging position. An installation of the electric wire cover 60 to the male housing 40 is disabled. In the state that both the housings 10 and 40 arrive at the regular engaging position, the locking part 61 is engaged with the part 49 to be locked, thereby allowing the electric wire cover 60 to be mounted at the male housing 40 and closing the back end face 10A of the female housing 10.