Each housing (10) includes terminal accommodating chambers (12), a communication opening (14) formed in an outer surface and communicating with the terminal accommodating chambers (12), and projections (16) projecting from a terminal accommodating portion (11). With the housings (10) placed one above the other, the projections (16) inserted in the terminal accommodating chambers (12) through the communication opening (14) are engaged with terminal fittings (20) in the terminal accommodating chambers (12) to retain the terminal fittings (20). Receiving portions (13) are provided in each housing (10) and each projection (16) includes a lock (18) to be engaged with the corresponding receiving portion (13) to hold the housings (10) in an assembled state.