To promptly achieve matching of engine output torque and pump input torque without requiring operation to determine an error between reference engine speed and actual engine speed.
This pump torque control device for a working machine is provided with a discharge pressure detector 17 for detecting discharge pressure of a variable displacement hydraulic pump 12, a tilting and rotating angle detector 19 for detecting a tilting and rotating angle of the variable displacement hydraulic pump 12, and an suction air amount detector 21 provided in an air supply line 5 for connecting an engine 1 with a turbosupercharger 4 and detecting suction air amount guided to the air supply line 5. The pump torque control device is further provided with a controller 15 for performing operation for calculating a pump input torque target value based on the discharge pressure detected by the discharge pressure detector 17, the tilting and rotating angle detected by the tilting and rotating angle detector 19 and the suction air amount detected by the suction air amount detector 21. A control signal corresponding to the calculated pump input torque target value is output to a regulator 13, so as to control the tilting and rotating angle of the variable displacement hydraulic pump 12.
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