An air-fuel ratio controller for use in an internal combustion engine, of a type having an exhaust gas sensor disposed in the exhaust passage, a control circuit and a solenoid valve having a valve seat in which passages open leading to the air bleeds of the slow and main systems of the carburetor, the controller being adapted to actuate a valve of the solenoid valve, in accordance with a signal derived from the exhaust gas sensor, into and out of contact with the valve seat, so as to simultaneously control the flow rates of bleed air in the air bleeds of the slow and main systems. A recess is formed in the cooperating surface of the valve seat or the valve, at a position between the openings of the passages in the valve seat. This recess communicates with a chamber which in turn communicates with the air inlet. Unfavorable mutual direct communication of the passages with each other is avoided, even when a slight gap is formed between the valve seat and the valve seated on the latter due to inclination of the valve seat or the like reason, because both passages communicate with the chamber through the recess.