PURPOSE: To ensure safe driving travel by releasing an automatic return mode when the present car speed at the time of the automatic return mode drops drastically to a certain degree in comparison with the maximum car speed detected at the time of the automatic return mode.

CONSTITUTION: A car speed operating means 12 operating a car speed from the pulse row signal of a car speed sensor 11, is equipped, and at the same time automatic return action starting means 15 such as a set signal inputting means 13, a cancellation signal inputting means 14 and a resuming switch, are equipped. And the maximum car speed at the time of an automatic return is memorized at an automatic return time car speed memorizing means 16 by means of output from the car speed operating means 12 and automatic return action starting means 15, and a car speed comparing means 17 decides whether or not a difference between the memorized car speed and the present car speed has become more than a predetermined value, and it is arranged that a release signal is outputted to an actuator 20 connected mechanically to a throttle valve 21 by means of a fixed speed travel releasing means 18, in a case in which a cancellation signal is inputted from the cancellation signal inputting means 14 or YES is decided by means of the car speed comparing means 17.