An air-fuel ratio control apparatus is basically provided with an exhaust system, a pair of sensors and a controller. The exhaust system includes an exhaust channel having a main catalytic converter, a bypass channel having a bypass catalytic converter, and a valve mechanism disposed in the exhaust channel to switch a pathway for exhaust gas from the exhaust channel to the bypass channel. The sensors output signals indicative of air-fuel ratios of exhaust flowing in their respective channels. The controller has first and second air-fuel ratio control sections that control an engine air-fuel ratio based on outputs of the sensors, respectively. The controller has a control mode switching section that switches control from the first air-fuel ratio control section to the second air-fuel ratio control section after a prescribed interval of time has elapsed from when the valve mechanism is switched from a closed state to an open state.