PURPOSE: To detect a stable vortex frequency signal and to detect an analog signal corresponding to a mean flow speed at the same time, by detecting the change in the flow of fluid due to the vortex by heat sensitive elements which are provided so as to widen an effective area.

CONSTITUTION: A pair of heating wires 31, which are provided behind a vortex yielding body 2, are approximately vertically stretched within a lateral width D of the yielding body 2. Then the wires are bent and stretched to the outside of the lateral width D in a V shape. Thus the effective area is widened. The heating wires 31 are also provided at the opposite side. The detection is performed in the wider area in comparison with the case the change in the flow speed is detected by dot or a piece of wire. Therefore the stable detection of the vortex signal can be expected. An electric signal corresponding to the mean flow speed can be concurrently detected by a part protruded from the width D. As a result, the stable vortex frequency signal can be detected, and the analog signal corresponding to the mean flow speed can be also detected.