The invention provides an electromagnetic flowmeter and a control method of an electromagnetic flowmeter. The electromagnetic flowmeter measures a flow rate of a liquid of a measurement target that flows in a magnetic field formed within a measurement pipe. The electromagnetic flowmeter includes at least one pair of detection electrodes configured to detect an electromotive force generated due toa flow of the liquid, and configured to output a flow rate signal of a magnitude of the detected electromotive force, a measurement circuit configured to supply an alternating current between the detection electrodes and an earth electrode, and a control calculator configured to control a frequency of the alternating current to be 1 kHz or more, and configured to calculate a conductivity of the liquid whose conductivity is 1 mS/cm or more based on the flow rate signal output when the alternating current flows between the detection electrodes and the earth electrode.