To detect flow rate with high accuracy for a long term using a vibration sensor for fluid which can sustain the detection characteristics for a long term without requiring any adjustment.

The flexure detecting section 6 of a flexure detecting means 8 magnetically detects the flexure of a magnetic membrane 5 caused by the pressure P1 of a fluid introduced into a first pressure chamber 3 and the pressure of a fluid introduced into a second pressure chamber 4 and a signal converting section 7 outputs an electric detection signal SD corresponding to the detected flexure of magnetic membrane 5. Since the signal converting section 7 is not exposed directly to the fluid, corrosion of the electric system is retarded and since a magnetic membrane is employed for detecting the flexure, fluctuation in the characteristics is suppressed thus suppressing the aging and providing a sensor suitable for long term use. Furthermore, the flexure detecting section 6 has low electric impedance and insusceptible to electric noise thus ensuring high reliability and a flow detector employing the flexure detecting section 6 can detect the flow rate with high reliability for a long term.