PURPOSE: To facilitate systematic alignment after cornering by constituting a front wheel accelerating mechanism to be forcively restored to a constant velocity condition upon detecting a rotating angle equal to or more than a definite one of a rotating angle sensor while being interlocked with cornering actuation.

CONSTITUTION: Based on the steering angle of a steering sensor 18 which is equal to or more than a definite one, a mechanism allows acceleration A to be switched to (engagement R1) via an actuator 20. And when a steering angle is returned back to one less than the definite angle on the part of the steering angle sensor 18, acceleration A is controlled by an output command (R) which allows constant velocity B to be switched to (engagement R2) while the aforesaid acceleration is being switched to (disengagement). Then, the mechanism functions based on the indication of a rotating angle sensor 5 when an angle determined by a double velocity release angle setting volume 19 is consistent with a rotating angle to the reference proceeding direction which is read in by the rotating angle sensor 5, control is executed by an output command S in such a way that (the engagement R1) of the acceleration A of front wheels is switched over to (the engagement R2) of the constant velocity B side via the actuator 20.