To prevent sudden start of a vheicle in the case where a driver erroneously operates an accelerator and a brake by suppressing the opening degree of throttle valve more than the step-down rate of a accelerating pedal corresponding thereto, when low speed degree of a vehicle is detected by the output of a speed detecting means.

When a vehicle is driven, the step-down rate of an accelerating pedal is detected, it is judge whether or nor an accelerating switch 15 is turned off and it is judged whether or not its speed is a prescribed value (for example 20km/h) or less when it is 'OFF.' In the case where the prescribed value and less is judged, operating speed of a throttle valve 14 is controlled. Restriction is applied to an opening degree so as to prevent the throttle valve 14 from fully opening to prevent danger that a vehicle is suddenly started against driver' s will when a driver mistakes an accelerating operation for a brake operation. Namely, the throttle valve 14 is opened slowly even when the accelerating pedal is stepped down rapidly.