PURPOSE: To measure the transfer function of a corrosion reaction circuit network over a broad frequency range, by imparting electric charge to a sample in a corrosive liquid, measuring the polarized potential and current, performing the frequency analysis of the output, and obtaining the phase difference.

CONSTITUTION: A sample metal piece 1, a reference electrode 2, and a counter electrode 4 are immersed in a corrosive liquid 4. Electric charge is imparted to the sample metal piece 1 from a charge imparting part 5 through the counter electrode 3. The current, which flows from the charge imparting part 5 to the metal piece 1, is detected by a current detecting part 7 and converted into a potential signal. The potential response of the metal piece is detected by a potential detecting part 6. Fourier transform of these signals is performed in a high speed Fourier transform part 8, the impedance at each frequency and the phase difference of the current and the potential are computed, and a transfer function is outputted.