PURPOSE: To economize power consumption of an oil hydraulic unit having a standby oil hydraulic pump installed by comprising an operation circuit in such a way that a pump under no load is stopped when an actuator is operating and a pump under load is stopped when the actuator is not operating.

CONSTITUTION: When a hydraulic cylinder OC is operating, two motors comprising M1 and M3, or M1 and M2, or M2 and M3 are turned into load operating conditions responding to the performance of the hydraulic cylinder OC, and one motor is not operated. On the other hand, when the hydraulic cylinder OC is not operating, one motor of M1, M2 and M3 are consecutively turned into operating state under no load, and the other two motors stops the operation. Therefore, when the hydraulic cylinder is not operating,two motors out of either P1, P2 and P3 are operating under no load, affecting no adverse effect to the performance of the hydraulic cylinder OC. When the hydraulic cylinder OC is under no load, one montor out of either hydraulic pumps P1, P2 and P3 is operating under no load. When the hydraulic cylinder OC is shifted to operating conditions, two motors can move to load operating conditions without causing delay.