To make the values of currents flowing in the sensor coils of pickups and the exciting coils of exciters larger.

A pickup holder holding the sensor coils of pickups 23, (24), 31, (32), an exciter holder holding the exciting coils of exciters 38, (39), and a converter 26 holding a control circuit driving the exciters 38 (39) and calculating flow rates from the outputs of the pickups 23, (24), 31, (32) are communicated with one another to form a sealed container for a cylinder to be measured, with all of conducting parts enclosed to make the currents, which the pickups 23, (24), 31, (32) output, larger, thus enhancing sensitivity; also, the currents supplied to the exciters 38, (39) are made larger to increase exciting forces.