Abstract: With a very simple arrangement, body composition impedance, which excludes contact impedance between the dermal surface of a patient and each electrode and body distal site surrounding composition impedance, is measured thereby measuring the amount of body fat with high accuracy. Two pairs of electrodes (four electrodes in total) are connected to a constant current circuit through analog switches respectively. The electrodes to which a constant current is applied are sequentially switched by control signals output from an arithmetic operation control unit. By use of output voltage signals from an operational amplifier, a CPU in the arithmetic operation control unit calculates the value of the body composition impedance by removing the contact impedance and the body distal site surrounding composition impedance.