PURPOSE: To measure a powder flow rate in wide range from low to high concn. ranges by providing interposingly a bent tube en route in a piping or using the bent part of the existing piping.

CONSTITUTION: In case that the solid-gas mixed phase fluid flows in the piping P, since the detecting end of a sensor 3 provided at an entrance part is depressed slightly from the inner wall of the tube, the powder scarcely impinges directly at the end. Therefore the sensor 2 catches the sound of mutual impinging of the powders passing the transverse section of the entrance part of the bent tube 1. Concerning the powder flow near the center part of the tube 1, large particles 8 can't make a turn in the tube 1 due to the large inertia force, and impinge at the inner wall surface of outside of the center part of the tube 1. Since the sensor 3 is provided so that the surface of the detecting end coincides with the inner wall of the tube 1, the particles 8 impinge at the sensor 3, the friction sound is generated, and is picked up at the sensor 3. Concerning the powder flow at the exit part of the tube 1, since small particles 9 impinge at inner wall of the tube near the exit, the particles 9 impinge at the sensor 3 and the friction sound is generated. The quantity of the particles 9 can be obtained similarly to the previously described case of the particles 8 from the intensity and frequency of this friction sound.