A constant speed regulator apparatus includes a vehicle speed sensing unit which detects a vehicle speed of an automotive vehicle. An idle switch unit detects an OFF state of a throttle valve. A throttle adjusting actuator adjusts a throttle opening angle of the throttle valve to vary the vehicle speed. A target speed determining unit determines a target speed by using the vehicle speed which is detected by the vehicle speed sensing unit immediately after the OFF state of the throttle valve is detected by the idle switch unit. An actuator control unit regulates the throttle adjusting actuator so that the vehicle speed is maintained at the target speed determined by the target speed determining unit.