To prevent occurrence of erroneous shifting in a reversing direction during foreward running.

When pumping hydraulic pressure of an oil pump is introduced to a hydraulic chamber 49 during running, which pump is interlocked with an output shaft that transmits power to a driving wheel, a front projection 48a of an interlock plunger 48 is engaged with a slide groove formed on a reverse accent shaft of a reverse accelerator unit 40, for regulating movement of a shifter arm 37 interlocked with a shift lever in a reversing direction. When speed of the running vehicle is low, or the vehicle is stopped, the pumping hydraulic pressure is lowered and the interlock plunger 48 retreats for disengaging the front projection 48a with the slide groove. Shifting in the reversing direction is thus enabled.