A wire cover (70) is arranged to cover a rear surface of a mat seal cover (50) and includes a lock (78) to be locked to a lock receiving portion (27) of a housing (10). The lock receiving portion (27) is arranged at a position corresponding to a lever (90) covering an outer surface side of a peripheral wall (24) of an accommodating recess (23). The lock (78) is locked to the lock receiving portion (27) from an inner surface side of the peripheral wall (24) of the accommodating recess (23). The mat seal cover (50) has an assembling detection surface (55) with which the lock (78) moving toward the lock receiving portion (27) comes into contact when the mat seal cover (50) is in a semi-assembled state without being locked to the housing (10).