PURPOSE: To measure mass flow rate by vibrating an omega-shaped pipe in which the fluid to be measured flows in the direction perpendicular to its traveling plane and detecting the rate of torsion generated between two symmetrically curved parts of the pipe.

CONSTITUTION: The straight parts 1' of an omega-shaped pipe 1 of a circular section are fixed respectively to a base 2, and their terminals are connected to a pipe line system, then the fluid F to be measured is flowed. A permanent magnet 4 is fixed to the end of the pipe 1 and an electromagnet 6 is disposed in opposition to the permanent magnet 4, so that the pipe 1 is vibrated in the direction orthogonal to the traveling palne of the fluid F. Also, a torque beam 7 is spanned and fixed between the maximum spacing position of the curved prts 1" of the pipe 1, and strain gages 8W11 are adhered to both surfaces and both ends thereof. As the pipe 1 vibrates, the vibration torque of the torsion of which the amplitude is proportional to the mass flow rate of the fluid is generated in the pipe, thereby causing the strain gages 8W11 to distort. These distortions are detected as the unbalance voltage of a bridge circuit, whereby the mass flow rate is measured.