Provided is a control unit (1) for setting, for respective electronic throttles (11) and (12) provided for respective cylinders, respective ranges of a difference between a target rpm and an engine rpm where the electronic throttles (11) and (12) are not operated as a first dead zone and a second dead zone, determining, for each of the electronic throttles (11) and (12), whether or not the difference between the target rpm and the engine rpm is in the dead zone, preventing the electronic throttle determined to have the difference in the dead zone from operating, and determining, for the electronic throttle determined to have the difference exceeding the dead zone, a control gain for the electronic throttle depending on the magnitude of the difference, thereby operating the electronic throttle.