Front shake preventing ribs (37) are provided at positions spread over the entire inner periphery of a front end of an inner housing (23) and contact a receptacle (14) of a male housing (10) to prevent shaking between an inner housing (23) and a receptacle (14). A wall (31) faces an opening edge portion of the receptacle (14) at a rear end of the inner housing (23) with respect to the connecting direction with the male connector (10). The receptacle (14) is formed with an annular rib (18) projecting in a connecting direction the connectors (10, 20) at a position to surround the inner housing (23) over the entire periphery. The wall (31) has an annular groove (32) that engages the annular rib (18) to prevent shaking between the connectors (10, 20).