An air-fuel ratio control apparatus is basically provided with an exhaust system, a first sensor and a controller. The exhaust system includes an exhaust channel with a main catalytic converter disposed therein, a bypass channel with a bypass catalytic converter disposed therein, and a valve mechanism disposed in the exhaust channel between the connection points of the exhaust channel to switch a pathway for exhaust gas from the exhaust channel to the bypass channel. The first sensor detects a property indicative of an air-fuel ratio of exhaust flowing in the exhaust channel at a point downstream of the valve mechanism. The controller adjusts an element temperature of the first sensor to a prescribed temperature or less during a prescribed interval of time from when the valve mechanism is switched from a closed state to an open state.