PURPOSE: To provide a control circuit permitting no energy loss such as pressure loss to occur even when the speed of or the supply pressure for the actuator is controlled.

CONSTITUTION: In a hydraulic circuit for a power shovel, each of paired running motors 11, 12, an arm hydraulic cylinder 13, a boom hydraulic cylinder 14, a bucket hydraulic cylinder 15, and a swing motor 16 is connected thereto with a corresponding one of ultrahigh speed on/off valves 17 to 22 for controlling the supply flow and the supply pressure through control of the proportion of their full closure and their full opening in one cyclic period, a preliminary ultrahigh speed on/off valve 23 being provided.