A waterproof rubber plug has a through hole through which an electric wire is inserted. The electric wire is connected to a terminal. An inner housing has a terminal chamber for accommodating the terminal. An outer housing has sidewalls for defining a chamber provided with a rear wall, into which the inner housing is fitted. A through hole, through which the electric wire is inserted, is formed on the rear wall so as to face the terminal chamber when the inner housing is inserted into the chamber of the outer housing. A recess is formed on the rear wall so as to communicate with the through hole and opened to the outside of the outer housing. A press-fitting member is engaged with the outer housing while press-fitting the rubber plug into the recess after the inner housing is completely fitted into the chamber of the outer housing, thereby sealing the electric wire and the terminal chamber.