PURPOSE: To achieve a higher measuring accuracy, by detecting a displacement of a metal diaphragm due to a difference in a Karman's vortex generated according to the flow rate as changes in the electric resistance.

CONSTITUTION: When a differential vortex pressure due to a Karman's vortex generated according to the flow rate of a fluid to be measured is introduced into lead chambers 12a and 12b through a different vortex pressure introduction holes 5a and 5b, metal diaphragms 9a and 9b are displaced differentially accompanied by the movement of a sealing liquid 16 as conducting liquid. As a result, the interval changes between the metal diaphragm 9a and 9b and fixed electrodes 11a and 11b to vary electric resistance value through the sealing liquid 16 therebetween. So to speak, the displacement of the metal diaphragm 9a and 9b due to differential vortex of the Karman's vortex is detected as change in the electric resistance between the metal diaphragms 9a and 9b and fixed electrodes 11a and 11b and a flow rate measurement signal is outputted from a flow rate detecting section 1.