This invention relates to a hydraulic circuit for working machines, provided with a hydraulic fluid source (1), at least one hydraulic actuator (3 or 13) adapted to be driven by the hydraulic fluid supplied from the hydraulic fluid source, flow rate control valves (4; 4A or 14; 14A) adapted to control a flow of the hydraulic fluid supplied to the actuator, and pressure control means (5; 5A or 15; 15A) for maintaining the pressure differences across the flow rate control valves on predetermined levels. The apparatus according to this invention has a first means (20; 23; 35, 36) for selectively producing one of a pressure equal to a load pressure and an intermediate pressure higher than the load pressure but lower than a supply pressure, on the basis of a load pressure on the actuator (3 or 13) and a supply pressure in the hydraulic fluid source (1), and outputting the resultant pressure as a control pressure; a second means (21; 27; 29; 34, 36) for operating the first means to specify a pressure to be selected as a control pressure, i.e. one of the pressure equal to the load pressure and the intermediate pressure; and a communication means (22) for introducing the control pressure to the pressure control means (5; 5A or 15; 15A). The pressure control means is adapted to maintain the above-mentioned pressure difference on the above-mentioned predetermined level when the control pressure is equal to the load pressure, and set the pressure difference to one lower than the predetermined level when the control pressure is the intermediate pressure.