PURPOSE: To shorten control time for a pump and a motor for eliminating oversteering by shortcircuiting the high pressure side circuits of left and right hydraulic drive units through an equalizing valve in steering.

CONSTITUTION: Left and right hydraulic drive units 1, 2 are provided respectively with variable pumps 3, 8, variable motors 4, 9 and shuttle valves 7, 12. Further, outlet ports 7a, 12a of both shuttle valves 7, 12 are connected to each other through pipe paths 14, 15 and an equalizing valve 13. And for example in the case of right steering, a solenoid of the equalizing valve 13 is turned off to interconnect both pipe paths 14, 15. Thus, the high pressure side circuits of the left and right hydraulic drive units 1, 2 are shortcircuited to eliminate the difference between capacities of both variable pumps 3, 8.