Disclosed is a device for injecting fuel into an intake air supply passage which is communicated with the combustion chambers of an internal combustion engine.The device comprises: a swingable throttle shaft having a hole formed therein along a longitudinal axis thereof and traversing an intake air supply passage; a throttle valve plate fixed to the throttle shaft for throttling the intake air supply passage so that the throttle valve plate can vary the opening of the air supply passage due to the swing of the throttle shaft; and a fuel injection outlet portion formed at the proximity of the surface of the throttle valve plate and communicated with one of the hole. Fuel supplied from the fuel injection outlet portion is uniformly admixed with the air flow which is caused to contract by the throttle valve plate.