PROBLEM TO BE SOLVED: To improve the reliability of a stress corrosion crack test for a metal material. SOLUTION: A test piece is installed S2 in a prescribed grain boundary corrosion crack environment, and a tensile force is applied to the test piece in the prescribed stress corrosion crack environment. Tensile tests S3 and S13 are conducted for the test period set, so that the maximum value of the depth of the cracks growing on the test piece becomes a set value or below, and the depths of the cracks are measured S4 and S14. The values, subtracted with the depth of the initial grain boundary corrosion crack, are divided by the test period, to calculate stress corrosion crack growing speeds S5 and S15.
