PURPOSE: To enable the adjustment of the length and distribution of a defect in an artificial defect test piece by applying a local pressure from te back of a metal plate with a coated layer thereon to make a defect on the coated layer.

CONSTITUTION: A metal coated layer 2 is formed on the surface of a metal substrate 1. Then, the metal substrate 1 is placed on a base 3 with the coated layer 2 facing the base and a local pressure is applied thereon from the back thereof to make an artificial defect on the surface of the metal coated layer. This local pressure can be given by pressing a steel ball, for example, a Brinell ball against the substrate. A defective crack of almost average length can be formed freely at the desired position on a test piece. The length or the like of the defective crack can be adjusted by controlling the components of the metal coated layer. In this case, it is preferable that the local pressure is applied on the test piece after it is placed on a metal plate 5 which is laid on a rubber plate 4 on the base.