PURPOSE: To provide a flowmeter which makes a vane contact a cam face favorably, and effects an accurate operation with less leakage of a liquid even when the rotation of a rotor is stopped or the rotational speed of the rotor is lowered.

CONSTITUTION: A plurality of vanes 18 mounted rotatably about the center of rotation along the center of rotation of a rotor 12 in the direction XY are mounted on the outer circumference of the rotor 12 arranged in a casing. An inner circumferential cam face 20 formed on the internal surface of the casing is allowed to abut an external end rim part of the vane 18 so that the inner circumferential cam face 20 contacts the outer circumferential surface of the rotor 12 at a specified position in the circumferential direction of the rotor. A fluid passage is formed to an fluid outlet 8 from a fluid inlet 6 passing at a circumferential position opposite to the specified circumferential position. A permanent magnet 22 is arranged right below the inner circumferential cam face 20 and an iron material 19c is buried into a tip rim part of the vane 18. The casing has a rotor passage detection sensor 24.