PURPOSE: To carry out work stably, by adjusting the hydraulic pressure of hydraulic operating fluid with an accelerator pedal interlocking type variable throttle valve, and operating the adjusted hydraulic pressure to a piston for traveling and a piston for working.

CONSTITUTION: The hydraulic pressure of hydraulic operating fluid from an oil pump 1 is adjusted by an accelerator pedal interlocking type variable throttle valve 15. The adjusted hydraulic pressure is operated to a piston 20 for working and a piston 30 for traveling in case of the traveling of a vehicle, and is operated to the piston 20 for working in case of working. The displacement of the pistons 20, 30 is transmitted to an injection quantity adjusting member 27. Thereby, the position variation of the member 27 against the number of rotations can be enlarged in the low and intermediate speed ranges of working, so that the working can be carried out stably.