On the basis of reference torque and torque correction amount output units (T1 and T2), a torque control command pressure is calculated so that the input torques of first and second pumps are increased. The calculated torque command instruction pressure is then supplied as external command pressure to the varying mechanism of a regulator used for the first and second pumps so as to prevent the input torques of the first and second pumps from being decreased more than necessary. As a result, even when three variable displacement hydraulic pumps are used with the discharge pressure of one of the hydraulic pumps reduced by a pressure reducing valve and further the input torques of the other two hydraulic pumps are decreased by that pressure, the engine output can be efficiently utilized, and the work rate does not decrease.