The present invention provides an apparatus for measuring electrical
impedance comprising: two input electrodes contacted to a subject for
measuring impedance; a difference amplifier to which two signals inputted
to the two input electrodes are inputted; a device for extracting a
common mode component of two signals inputted to the two input
electrodes; the third electrode contacted to the subject for measuring
impedance; the first multiplier to which the common mode component is
inputted; the first filter coupled with the first multiplier; the second
multiplier coupled with the first filter; wherein a feedback signal
outputted from the second multiplier is inputted to the third electrode.