PURPOSE: To eliminate wrong operation and promote safety, by stopping the control of the degree of opening of a throttle valve when it is detected that at least two of a setting, an accelerating and a presetting instructions for the degree of opening of the throttle valve are simultaneously produced.

CONSTITUTION: A setting switch 38 which generates a setting instruction, a resuming switch 30 which generates an accelerating instruction and functions to instruct the resumption of the temporarily stopped control of the degree of opening of a throttle valve, a presetting switch 80 which generates a presetting instruction, etc. are connected to a control circuit 90. The throttle valve is regulated by an actuator 28 in accordance with the output signal of the control circuit 90 to govern the speed of a vehicle. When the switches 30 and 38 or 80 are simultaneously put into operation, a self-holding circuit 34 is put out of operation through OR gates 108, 60 by the output "1" of an AND gate 102 or 104 to stop the control of the vehicle speed. The vehicle speed control can be likewise stopped when the switches 38, 80 are simultaneously put into operation, too.