An electromagnetic flowmeter using a square wave excitation method includes a differential amplifier which outputs a detection signal; an analog-digital converter which converts the detection signal into a digital detection signal; a timing control circuit which generates a sampling signal for sampling the digital detection signal; an calculation unit which executes a flow rate calculation process and a abnormality judging process at a same time. The flow rate calculation process acquires a flow velocity output signal by sampling the digital detection signal in a flat portion in a positive/negative excitation section. The abnormality judging process acquires a differential output signal by sampling the digital detection signal in a rising/falling portion in the positive/negative excitation section, and obtains a differential noise from the flow velocity output signal and a differential output signal, and judges abnormality of the exciting current by comparing a differential noise with a detection threshold level.