A cover plate for covering exposed conductive wires of a flat cable is attached to a surface of an attaching plate for holding the flat cable, and insert molding is performed in such a manner that the cover plate is included. Therefore, direct contact of a portion of flows of synthetic resin for use in performing insert molding that flows along a surface of the attaching plate for holding the flat cable with conductive wires of the flat cable can be prevented. Moreover, if the synthetic resin introduced into another surface of the attaching plate for holding the electric wires flows in joint portions between the conductive wires, the conduction wires of the flat cable are pushed against the cover plate due to the flow of the synthetic resin so that the conductive wires of the flat cable are supported. Thus, the conductive wires of the flat cable can be protected from excess stress when the insert molding operation is performed. Thus, breakage of the conductive wires of the flat cable can be prevented.