An apparatus includes a first electrode connected to one end of a cell within a living body, a second electrode connected to the other end of the cell within the living body. A measurement unit selectively extracts a voltage induced to the first and second electrodes depending on the current applied to the first and second electrodes. A charge storage unit stores a relative potential corresponding to a voltage difference between the first and second electrodes. An A/D conversion unit configured to convert a signal corresponding to the relative potential into a digital signal. An impedance calculation unit configured to calculate interfacial impedance of the first and second electrodes using the digital signal from the A/D conversion unit and the current applied to the second electrode.
