To reduce instant impact load at the time of engagement of speed change clutches when an engine is returned from a rest state, in the engine in which the engine speed is reduced at the time of temporary rest of a work, in order to reduce noise and suppress the fuel consumption.

When it is detected that a work of a vehicle is switched from a work-load state to a no-load state, the engine speed is reduced to a first, prescribed engine speed, and after the first, prescribed engine speed is held for a first, prescribed time, the engine speed is further reduced up to a second, prescribed engine speed. When it is detected that the engine speed is returned to the work load state, while the engine maintains the first prescribed engine speed or the second prescribed engine speed, the limitation of the engine speed to the first prescribed engine speed or the second prescribed engine speed is released from the detection after the second prescribed time has elapsed.