PURPOSE: To improve converging ability of idle rotation through fluctuation of engine torque with high follow-up by a method wherein a physical amount considered to have a linear relation with torque, shown in a figure, of an engine is used as an operation amount of proportional-plus-integral control during idle control.

CONSTITUTION: During control of an engine by an ECU, after an actual process intake amount Ga is first calculated at S101, a movement amount FBN is partially added to the actual number Ne of revolutions of an engine at S102 and further a target number of revolution moving amount ΔNe is subtracted to calculate the number IRPM of evolutions indicated in a map. By means of the IRPM serving as a parameter, a fundamental stroke intake air mount Gabase is set by using a map at S103 and from he Gabase, a target stroke intake air amount Gaset is calculated at S104. Thereafter, based on a Gaset, a cylinder inflow air amount and a pass air amount of an idle control valve are calculated at S108 and S100. A final duty ratio outputted to an idle control valve is calculated.