PURPOSE: To enhance reliability of engine operation, by using a DC motor for a throttle actuator, and controlling a throttle valve at the time of deceleration by means of a control unit in which required characteristics for closing the throttle valve are stored in its memory and to which signals relating various operational conditions of an engine are furnished as inputs.

CONSTITUTION: A throttle valve 3 opened in response to the depth of depression of an accelerator pedal is provided in a carburetor 2 of an engine 1, and a throttle actuator 6 with a touch sensor 5 held in contact with a throttle lever 4 is constituted by a DC motor. A control circuit 16 is furnished with signals relating to various operational conditions of the engine in addition to a throttle valve closing signal produced by the touch sensor 5 and gives a control signal to the actuator 6. When deceleration of the engine is detected from switching of the touch sensor 5 from OFF to ON, the control circuit 16 controls the actuator 6 to close the throttle valve at the speed pre-stored in the circuit 16. By employing such an arrangement, a diaphragm means can be omitted and general-purpose properties can be enhanced since the above arrangement can be applicable to various types of engines.