PURPOSE: To simplify a control work and save the labor by a method wherein a contact detecting means is connected to a control circuit, an actuator to rotate an accelerator lever to a given position on the high speed side or the low speed side is connected to the control circuit, and the number of revolutions of an engine is controllable.

CONSTITUTION: A protrusion part 12a is arranged to the support member 12 of a rear bumper 6 such that the contact of a limit switch 18 is capable of making contact with only the protrusion part 12a to form a means to detect contact with a pile. The limit switch 18 is connected to a control circuit in a control box 11. An operation switch 15 arranged on a control panel and a solenoid 17 are connected to the control circuit and the solenoid 17 is connected to a throttle arm 19. One end of a wire 20 is connected to the throttle arm 19, and the other end of the wire 20 is connected to an accelerator lever 14. This constitution causes automatic adjustment of the number of revolutions of an engine to a high speed during a control work and to a low speed during a nonwork and saving of labor for works.