PURPOSE: To improve the measurement accuracy of a Coriolis mass flowmeter with a simple circuit configuration by controlling the generation of a compensating signal so that a Coriolis signal detected from reference vibrations can become zero and using the signal corresponding to the compensating signal as a mass flow rate signal.

CONSTITUTION: A fluid to be measured is made to flow by vibrating a tube 11 at reference vibrations and a Coriolis signal which is proportional to a mass flow rate to be measured and has a phase difference is outputted against a reference signal VF by strains generated in a metallic plate 13. The Coriolis signal is inputted to a synchronous rectifier circuit 19 across which a reference voltage having a phase difference of 90O against the reference vibrations is applied and further inputted to a deviation amplifier 21 as a Coriolis detecting signal VCD. Since the amplifier 21 makes an oscillator 16 output a compensating signal VC having the same value as the signal VCD to an adder 17 and subtractor 18 by giving a control signal VG to the oscillator 16, a sum signal AA and difference signal AS are impressed upon exciters 12A and 12B so that the signals AA and AS can become opposite in phase against the Coriolis component and the signal VCD is offset by twisting the tube 11 in the opposite direction against a torsional axis. The compensating signal VC is detected as a mass flow rate signal.