To improve a hydraulic circuit, including a structural change of an feed pump and a revolving motor, so as to increase the efficiency of a hydraulic system, during excavation work in the state of abutment on the lateral surface of a ditch by an excavator.

This excavator has an integral-hydraulic pump which comprises first and second pumps P1 and P2 for driving an excavation section and a traveling section, and a third pump P3 for driving a revolving section. The overall length of the pump is kept short by employing the third gear-type pump, and a variable displacement motor is employed as the revolving motor of the revolving section, so that an efficient operation can be realized during the excavation work in the state of the abutment on the lateral surface of the ditch.