PURPOSE: To replenish surely pressurized oil to a low pressure side main pipe line even in abrupt change-over of a direction change-over valve by providing throttles in one pair of pilot pipe lines of an auxiliary change-over valve and a check valve in the other pair to afford communication to or shut off the remaining pilot pipe lines according to a position of the auxiliary change-over valve.

CONSTITUTION: A valve body 26 of an auxiliary change-over valve 21 is provided with left and right oil grooves 41A, 41B, and oil chambers 29A, 29B as a hydraulic pilot section are connected to main pipe lines 3A, 3B through pilot pipe lines 43A-45A, 43B-45B between a counter balance valve 7 and center joint 13. Also, throttles 46A, 46B and check valves 47A, 47B are provided on the way of the pilot pipe lines 43A, 43B; 44A, 44B and the pilot pipe lines 45A, 45B communicate to each other and are shut off from each other through the oil chambers 29A, 29B and oil grooves 41A, 41B according to a position of a spool 28. Thus, the auxiliary change-over valve 21 can beheld near the neutral position to replenish pressurized oil to a low pressure side main pipe line and prevent cavitation even if a hydraulic motor 1 is abruptly reversed.