PURPOSE: To measure the flow rate accurately over a wide range of current velocity by fixing two wedges in a chamber, forming a water collecting path in a part inside wedge and detecting a fluid jet through a detection hole.

CONSTITUTION: An inlet nozzle 8 and an outlet 25 are provided at a body section 7 and a fluid jet flow for generating two reverse turn primary vortex and a plurality of secondary vortexes around the center line 10 of a fluid jet is formed through the nozzle 8. Wedges 11, 16 are fixed in a chamber 9 while having linear outer walls 13, 18 and convex inner walls 12, 17 and a gap 20 is formed between the inner walls 12, 17. The fluid jet partially passes through the gap 20 but the majority thereof flows over the top parts 14, 19 and then flows downward along the outer walls 13, 18. High and low pressures are generated alternately through movement of vortex and detected by means of a transducer coupled with pressure holes 21, 22.