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 bottom wall, into which the inner housing is fitted. A through hole, through which the electric wire is inserted, is formed on the bottom 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 bottom wall so as to communicate with the through hole and opened to the outside of the outer housing, into which the rubber plug is fitted after the inner housing is completely fitted into the chamber of the outer housing, thereby sealing the electric wire and the terminal chamber.