An internal combustion engine having an intake passage that is closed at the time of engine starting operation wherein a holding time for completely closing a throttle valve is made as long as possible within such a range that the engine does not fail to be started. The throttle valve is held at its full-closure position when an ignition switch is turned on. Then, at the time of engine starting operation, an amount of air consumed by the engine is calculated based on a cumulative rotational speed of the engine, a cylinder volume of the engine, and a parameter of volumetric efficiency corresponding to an engine rotational speed, and, if so, the throttle valve is opened to a predetermined opening degree.