In a mat seal cover of a waterproof connector, waterproof pins are provided inside through holes of the waterproof connector and are configured to close terminal insertion holes of a connector housing. The waterproof pins are retained in the through holes by pin retention portions. Coupling portions between the pin retention portions and inner circumferential walls of the through holes are disposed more closely to the front side in the pushing direction of the punching jig than abutment surfaces at rear ends of the waterproof pins against which the punching jig abuts, and rear end faces of the pin retention portions are inclined faces extending from the abutment surfaces toward the coupling portions and inclined to the front in the pushing direction of the punching jig.