To provide a magnetic dielectric flowmeter and a method for operating magnetic inductive flowmeter designed so that detection and indication of a slippage, from a state particularly calibrated as a result of a problem in an amplifying passage can be performed during the operation of the magnetic dielectric flowmeter by enabling easy calibration.

This magnetic dielectric flowmeter comprises a test voltage power source and a comparator. The test voltage power source generates a test voltage, the test voltage power source is connected to an amplifier so that the test voltage is sent to the amplifier and superimposed on a voltage detected by an electrode. The comparator is connected to the amplifier so that the output voltage of the amplifier is sent to the comparator, and the comparator compares the output voltage of the amplifier with a reference value.