A pair of thin-walled portions 6 are formed on packing 3 between a seal lip portion 92 and a vent hole in a connector housing 1. A pair of short-shot preventing ribs 8 are located contiguously to the thin-walled portions 6. The short-shot preventing ribs 8 are formed in a mold between the seal lip portion 92 and the vent hole (vent core 5), and a packing material is allowed to reach the vent hole via a narrow gap between each short-shot preventing rib 8 and the connector housing 1. Consequently, the flow resistance of the packing material increases, so that the packing material is preferentially filled in seal lip portions 91 and 92. The short-shot preventing ribs 8 may be formed on the connector housing 1 instead of the mold. The pair of short-shot preventing ribs 8 are formed, and the packing material is allowed to reach the vent hole.