Patent ID: 7878770

Claim:
A hydraulic circuit of construction machine comprising: operation means; a controller for outputting a command current based on an operation amount of the operation means; an electromagnetic proportional pressure reducing valve actuated by the command current outputted from the controller; and a hydraulic spool valve actuated by a secondary pressure from the electromagnetic proportional pressure reducing valve, the spool valve being configured to change a pump pressure in response to a change in an opening area of the spool valve, wherein a degree of change in the pump pressure by the hydraulic spool valve to a change in the proportional valve command value exhibits at least one inflection point at which there is an inflection in the degree of change in the pump pressure for a predetermined change of the proportional valve command value; the controller having correction processing means for correcting the proportional valve command value, comprising: means for comparing, at the at least one inflection point, a detected actual proportional valve command value to a theoretical proportional valve command value at which the set pump pressure is to be obtained in the case that a tolerance of the secondary pressure with respect to the proportional valve command value does not exist, and means, based on the comparison, for performing a correction to compensate for a difference between the detected and theoretical command values at the inflection point.