PURPOSE: To accurately and easily perform the corrosion test of a metal in a very short time by arranging a pair of metallic test pieces in a liquid at a prescribed space, applying an AC voltage across the test pieces and measuring the increasing rate of a flowing current for an elapsed time.

CONSTITUTION: A pair of test pieces are made of a metallic material and dipped in an objective solution 2 as electrodes Ia and Ib. An impedance meter 3 is connected between the electrodes Ia and Ib and an impedance between the electrodes Ia and Ib is obtained from the AC power supply 4 and the ammeter 5 of the meter 3. Changes in the impedance are recorded in an X-Y recorder 6 and the changing rate of the impedance after a prescribed time is obtained. When the corrosion of a metal is severe, the increasing rate for time of an ion density in the solution is large and, accordingly, reduction in the impedance is extreme. Thus, by measuring changes in the impedance or in a flowing current, the corrosion resistance of the metallic material and the degree of the corrosivity of the solution can be obtained.