PURPOSE: To automatically change a vehicle speed without use of a fluid torque converter with the speed change made more smooth, and with the acceleration and deceleration characteristics made more excellent by providing an RPM control means for controlling engine RPM independently of acceleration operation.

CONSTITUTION: RPM N of an engine 1 and an intake negative pressure Vc in a suction pipe 4 are respectively entered from a rotation sensor 6 and an intake negative pressure sensor 7 to a control unit 10, while RPM n of a propeller shaft 9 entered from a vehicle shaft RPM sensor 8 to the control unit 10. The control unit 10 incorporates the RPM N, the intake negative pressure Vc, the vehicle shaft RPM n, and a load signal L indicative of the amount of operation of stepping to an acceleration pedal 15, and delivers an operation signal to a throttle valve actuator 3 to specify the opening of a throttle valve 14. In addition, the control unit delivers a signal to injectors 5AW5D to specify the amount of fuel supply whereby an air-fuel ratio and the engine RPM can be controlled.