A connector housing includes a plurality of terminal chambers into for respectively accommodating a terminal provided with an electric wire. A mat-shaped rubber plug is attached to a rear end portion of the connector housing. In the rubber plug, recessed portions are formed so as to remain cylindrical protrusions each having a through hole through which the electric wire is inserted. A rear holder is attached to the rear end portion of the connector housing to retain the rubber plug thereat. The rear holder includes projections each configured so as to compress the associated protrusion of the rubber plug in the diameter direction of the electric wire as being inserted into the associated recessed portion of the rubber plug. The rubber plug includes at least one protrusion block formed by integrating adjacent cylindrical protrusions.