In the case of non-invasive measurement of bioelectric potential from body surface, the influence of the skin impedance has been investigated by using strict equivalent circuits of skin impedances. The relationship between the characteristic of skin impedance and the wave distortion was made clear. Furthermore, in the case of electrocardiograph, the shift potential of indifferent electrode to standard potential was obtained by means of simulation, and the distortions caused by connective resistances of a central terminal and skin impedance were quantitatively explained.