PURPOSE: To accurately control air/fuel ratio regardless of introduction of evaporated fuel and purging air to an engine.

CONSTITUTION: An air flow Q sucked into an engine 1 through a throttle valve 5 is measured by means of an air flow meter 4. Further, an air flow Qe flowing through an evaporated fuel purge passage 13 is estimated from the engine operating condition. A basic fuel injection quantity Tp is computed based on the sum of these air flows (Q+Qe). Meanwhile, an evaporated fuel quantity Tpe in the evaporated fuel purge passage 13 is measured by means of a gas sensor 15, and the evaporated fuel quantity Tpe is subtracted from the basic fuel infection quantity Tp. The fuel injection quantity from a fuel injection valve 6 is controlled based on this value (Tp-Tpe).