To improve a convergence property at a target engine speed by computing an offset amount of the target engine speed in response to a deviation between the real engine speed and the target engine speed, and changing the target engine speed while changing the offset amount in response to the fluctuated amount of the engine speed.

In the case of the idle operation, a deviation ΔNT is computed by an engine speed deviation computing unit 86 on the basis of a target engine speed NT set by a target engine speed setting unit 84 in response to the operating condition and the real engine speed NE detected by a crank angle sensor 38. A change deviation computing unit 94 computes the offset amount of the target engine speed in response to the computed deviation ΔNT, and the offset amount is changed in response to the fluctuated amount ΔNE obtained by an engine speed fluctuated variable computing unit 90, and a feedback control unit 88 is indicated so as to change the target engine speed to a new target engine speed based on the changed deviation ΔNTM. A deviation control unit 96 limits the offset amount on the basis of the engine speed NE and the fluctuated amount ΔNE thereof.