A vortex flowmeter wherein a main body and a fitting plate with a by-pass are integrally formed with each other and the fitting plate placed at an outlet of a passage of small diameter and of a constant section extending from an inlet of a large diameter with a continuous contraction. The passage in the main body includes a vortex generator and a vortex sensing means for detecting a vortex produced by the vortex's generator. The by-pass line is composed of a plurality of round through-holes arranged in a circular portion of the fitting plate.
