PURPOSE: To correct the position of a steering handle displaced from the right position by providing a working oil flowing means which is used for compensate the position of the steering handle, in an oil pressure line which connects a steering unit to a steering wheel driving actuator.

CONSTITUTION: When a steering unit 2 is driven by the operation of a steering handle 1, oil pressure from a pump 7 is sent into one half of a steering cylinder 4. The cylinder 4 therefore has the steering wheel steered in the same direction as that in which the steering handle 1 is operated. When the steering handle 1 is not in the forward traveling neutral position even if the steering wheel is held in said forward traveling neutral position, because oil leaks inside the steering unit 2, a manual change-over valve 15 which is disposed in oil pressure lines 5 and 6 is changed over to either one of positions to have working oil drained into a tank 8 from one of the oil pressure lines 5 and 6. Thus, the steering handle 1 can be idled and put into the neutral position without shifting operation of the steering cylinder 4.