To secure durability of a ring gear, a self-starter motor and a battery when stopping idling of an engine.

This intake air throttling device 1 of the engine is provided with a cylinder 3 having plural pistons 2A, 2B and operating in a multistage form, a throttle valve 6 operating in a multistage form for setting at least an intake air passage 5 of the engine 4 to full opening, full closure and one to plural intermediate opening by interlocking with operation of this cylinder 3, plural solenoid valves 7A, 7B arranged for regulating respective-stage operation of the cylinder 3 and plural pressure accumulating chambers 8A, 8B arranged between these respective solenoid valves and the cylinder. The throttle valve 6 is fully closed at idling stopping time to eliminate compression resistance, and the throttle valve 6 is held in full closure up to restarting time of the next time by pressure stored in the pressure accumulating chambers.