A retainer (40) has side plates (45) that slide against sliding-contact surfaces (29) of a female housing (20). Each sliding-contact surface (29) has an obliquely extending guide rib (33) and a locking projection (36) above the guide rib (33). The inner surface of each side plate (45) has a guide groove (46) into which the guide rib (33) is fittable and a locking hole (50) into which the locking projection (36) is fittable. Terminal fittings (11) are inserted into cavities (25) of the housing (20) and then the retainer (40) is pushed along the guide ribs (33) to a full locking position where the front edges of the side plates (45) contact the front edges of the sliding-contact surfaces (29) and the locking projections (36) are located in the locking holes (50) to doubly lock the terminal fittings (11) in the cavities (25).