A traveling hydraulic working machine has a target revolution speed of an engine commanded by an input and sensors for detecting an operating situation of a hydraulic actuator and an operating situation of a traveling system. A prime-mover revolution speed control modifies the target revolution speed of the prime mover when the operating situation of the hydraulic actuator and the operating situation of the traveling system come into respective particular states, and controls the revolution speed of the prime mover, With the traveling hydraulic working machine, in the combined operation of traveling and working a hydraulic actuator, work can be performed on the basis of the engine revolution speed intended by an operator. When a working load varies, the engine revolution speed is automatically controlled.