A detector (70) movable from an initial position to a detection position is mounted on a housing main body (11). The detector (70) includes a resilient arm (72) resiliently deformable in a height direction. The resilient arm (72) contacts a lock arm (12) from behind before the housing main body (11) is connected to a mating housing (50) to prevent a forward movement at an initial position. When the housing main body (11) is properly connected to the mating housing (50), the detector (70) reaches a detection position where the resilient arm (72) enters a deformation space (25) by being pushed forward from the initial position. At the initial position, the resilient arm (72) applies a pre-load to the lock arm (12) in the height direction.