To provide a waterproof connector backlash of which can be prevented without complicating the structure, and with no difficulty of design.

When a waterproof connector 10 and a mating connector 100 are fitted, a mating hood 110 enters between a fitting cylindrical portion 22 and the housing body 21 from forward, and a seal ring 60 is held elastically between the hood 110 and the housing body 21. The seal ring 60 has a seal lip 62 which is collapsed by adhering elastically to the inner peripheral surface of the hood 110 on the opening side when fitting, and a backlash filling portion 64 located forward of the seal lip 62, and filling the gap to the hood 110 by abutting against the inner peripheral surface of the hood 110 on the rear side in the front and rear direction when fitting.