PURPOSE: To prevent the function from degrading even when flow disorder occurs in the upper stream by setting a net crossing a fluid flowing main route in the fluid flowing main route in the upper stream of a fluid introducing route.
CONSTITUTION: An introducing flow route 7 which is larger than a flow route 2a of a nozzle 2 and becomes narrower gradually toward the nozzle 2 since flow rectifying plates 6 are formed on both sides of a center line J in the upper stream of the spraying nozzle 2 is formed on the center line J. In the upper stream of the flow route 7, a fluid flowing main route 8 which is expanded more than the flow route 7 is formed and a plurality of nets 9 are set in the flow route 8. These nets 9 are attached to a plurality of slits 10 formed in the inside of the flow route 8 and arranged in parallel each other so as to cross the flow route 8. Even if there is flow disorder in the flowing-in side, it is damped owing to collision against the nets 9 at the time of passing the nets 9 formed in the fluid flowing main route 8. Consequently, despite the flow disorder in the flowing-in side, the fluid vibration stably occurs in the flow route expanded part 4 and the high function as a flow meter is achieved.