A mat seal device for preventing water from entering an electrical connector through an opening provided for cables to be inserted into the connector. The device includes an elastic mat that plugs an opening in the connector. A peripheral edge seal of the mat seals between the mat and an inner surface of the connector housing. Cable insertion holes receive cables into the connector and prevent moisture from passing through the holes around the cables received in those holes. Each cable insertion hole includes annular sealing ribs that elastically enlarge when receiving a cable and seal against an outer surface of the cable. Recesses formed in front and back surfaces of the mat adjacent the cable insertion holes relieve expansion of the sealing ribs.
