Negative control of a split pump having a single swash plate consumes less energy than conventional negative control. A hydraulic circuit (1) for a construction machine is adapted for control of a split pump (111) the discharge volume of which can be reduced according to the magnitude of an external signal pressure. The hydraulic circuit (1) is provided with switching valves (118, 124) for controlling actuators (119, 120, 125, 126, 127), and also with control valves (115, 116) which can feedback, as external signal pressures, back pressures caused by the center bypass flow rates of two systems to the split pump (111). Further, the hydraulic circuit (1) is constructed such that, of the external signal pressures, a minimum pressure (external signal pressure (114)) selected by a low-pressureselecting valve (131) is fed back to the split pump (111).