To provide a thermal load suppressing device for a working machine capable of suppressing an excessive thermal load caused by exhaust gas of an engine without carrying out input torque control of a hydraulic pump.

An engine 1 is provided in a hydraulic excavator for driving the variable displacement hydraulic pump, a turbo type supercharger 4 is connected to a discharge line 6 for exhaust gas from the engine 1, and a supercharging pressure reducing means is provided for reducing a supercharging pressure of intake air after supercharging when an intake air temperature after supercharging by the turbo type supercharger 4 or a temperature of the exhaust gas introduced into the discharge line 6 becomes a temperature capable of applying an excessive thermal load. For example, the supercharging pressure reducing means is composed to include an after supercharging intake air temperature detector 14 detecting the after supercharging intake air temperature, and a supercharging pressure control valve 12 carrying out control of reducing the supercharging pressure of the after supercharging intake air when it is detected by the temperature detector 14 that the after supercharging intake air temperature or the exhaust gas temperature is the temperature capable of applying the excessive thermal load.