Abstract: 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, apparatus 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, apparatus 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 apparatus 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 apparatus for presetting a set value corresponding to the pressure difference, in o