PURPOSE: To change the rated number of revolution of an engine with a simple operation while setting a speed fluctuation rate within a proscribed range.

CONSTITUTION: The rotary part 8 of a governor device G is interlockingly connected to the rotary shaft of an engine E through a speed change gear 21. The speed change gear 21 is interlocked with a rated number of revolution setting lever 27. The change gear ratio of the speed change gear 21 is reduced by operation for changing the rated number of revolution setting lever 27 to a high speed side HS. On the contrary, the change gear ratio of the speed change gear 21 is increased by operation for changing the rated number of revolution setting lever 27 to a low speed side LS.