PURPOSE: To prevent control delay so as to improve responsiveness by estimate- compensating vehicle speed fluctuation due to delay in engine response by the addition of click signals.

CONSTITUTION: A click signal adding means 22 inputs a throttle opening control signal to additionally output a click signal increasing a throttle control amount by a specified amount for a time according to the opening/closing direction of throttle to a throttle opening control signal in a changeover point in a throttle opening/closing direction and to output the signal in itself except the changeover point. A throttle control means 24 controls the opening of throttle according to the output signal of a click signal adding means 22. A throttle actuator operated largely in the changeover direction for a time, so that estimation- compensation of vehicle speed fluctuation caused by delay in engine response, and it is possible to have a constant speed running controller for a vehicle excellent in responsiveness without delay in control.