PURPOSE: To mount a test piece and a corrosion crack detector in an integrated cassette form by arranging a plurality of test pieces not subjected to notching processing in series and applying load from one end to detect the displacement of each test piece as a change of the quantity of reflected laser beam.

CONSTITUTION: A test piece 12 is set to the same state as the surface of an actually used material not subjected to notching processing and formed into a C-shape set to a stress corrosion crack generating condition generating tensile stress by the load of a wt. 15. A plurality of the test pieces 12 are used in order to quantitatively process data as statistical quantity with due regard to the irregularity of the life of a material due to stress corrosion cracking and arranged in series in order to generate the same stress by a single stress load mechanism. A glass plate 16 provided with graduation lines is adhered to the side surface of the wt. 15 and irradiated with laser beam by a laser beam fiber 17 to detect the presence of the generation of the crack of each test piece 12 on the basis of reflection intensity and analytical operation is performed by remote operation. By this method, the test pieces 12 and a corrosion crack detector are formed into an integrated cassette form to simplify operation.