PURPOSE: To prevent the malfunction due to the variance of temperature or the like by using a partitioning plate to detect the variance of pressure due to a Karman's vortex street as a torsional stress of a torque tube.

CONSTITUTION: A vortex generating body 2, a torque tube 3b, a torque tube fixing part 3a, a pressure receiving plate 3c, and a distortion sensor 3d are attached to a main body part 1 inserted to a duct. When a fluid to be measured is flowed into the duct, a Karman's vortex street is generated in the downstream side of the vortex generating body 2 to cause a variance of pressure. When this variance of pressure is introduced to two chambers partitioned by the pressure receiving plate 3c from a pressure introducing port 3b, a periodical pressure difference is generated between both faces of the pressure receiving plate 3c, and the torque tube 2b is torsionally oscillated by this pressure difference. This torsional stress is detected by a distortion sensor 3d.