The invention provides an HC-discharge suppressing device and an operational method of suppressing the discharge of HC for a vehicle equipped with an engine that has an exhaust system including an HC adsorbent and an HC oxidation catalyst and that is stopped temporarily upon fulfillment of a predetermined condition for operating the vehicle. The planetary gear assembly includes a ring gear which, when allowed to rotate, effectively disconnects the drive motor from the cable drum. A doped silicon semiconductor substrate is covered with variable thickness silicon oxide regions on the surface thereof with junctions between the variable thickness regions.