When an idle speed control is implemented, an engine speed is computed based on an output signal of a crank angle sensor at a specified processing angle interval, and a time interval corresponding to the specified processing angle interval is computed. Then, the engine speed is filtered at a specified processing time interval, and a feedback amount (throttle opening correction amount) is computed based on a deviation of an engine speed filtered by a filter portion from a target engine speed. A time constant of a filtering processing is established according to the processing angle interval. Therefore, a filtering processing and a feedback control processing are performed in synchronization with each other, and an instability of an output of the feedback control (feedback amount) can be reduced.