In an automatic powder feeding apparatus of the type that the apparatus comprises a sensor nozzle for blowing a carrier fluid into an inlet of a detector tubular passageway having an inlet and an outlet, means for detecting a pressure difference between an inlet side pressure detecting port provided upstream of the outlet of the sensor nozzle and an outlet side pressure detecting port provided at the outlet of the detector tubular passageway, means for shunting a part of the carrier fluid to the inlet side pressure detecting port and regulating a pressure at the outlet of the detector tubular passageway, the means for regulating a pressure at the outlet of the detector tubular passageway being an injector connected via a valve to the outlet, and an automatic control valve having the pressure difference applied as its input and a flow rate of a driving fluid of the injector issued as its control output and including means for presetting a set value corresponding to the pressure difference, in order to obviate a transient increasing phenomenon of a powder flow rate occurring upon starting for recommencing an operation from an operation stop condition and to obtain a stable powder flow rate from the moment of starting, the automatic control valve and the outlet side pressure detecting port are connected with each other via a three-way valve.