Abstract: A relay 201 is provided for opening and closing the signal path connecting the measurement circuits and an electrode, and a relay 213 is provided for opening and closing a DC power line extending from an AC-DC adaptor 3 connected to a commercial AC power supply 5. In the measurement of the impedance, before supplying the current through the body of the subject, the relay 213 is opened to disconnect the commercial AC power supply 5 from a main unit 2 and a personal computer 1 so that the circuits are driven by the DC power from a battery 102. After that, the relay 201 is closed to connect the measuring circuit with the electrodes 10, 11, a weak current is passed through the body of the subject via the electrodes 10, and a voltage generated in the body by the current is measured with the electrodes 11.