A housing (10) includes a lock arm (31) for resiliently connecting and holding a mating housing (90). A detector (60) is movable to a standby position and a detection position with respect to the lock arm (31), and includes a resilient arm (62) to be resiliently locked by the lock arm (31) at the standby position. The lock arm (31) includes colliding portions (43) arranged at both sides of a front part of the resilient arm (62) and projecting farther forward than a front end of the resilient arm (62) and configured to contact a wall surface of the housing (10) or the mating housing (90) by a resilient returning movement of the lock arm (31) when the detector (60) is at the detection position.