PURPOSE: To improve reliability in inspection by performing black color oxidation of the main body of a multilayered wiring board wherein a through hole is formed, and thereafter performing the inspection.

CONSTITUTION: At the stage before the inspection of the inner layer of a multilayered printed wiring board, a through hole 24 is formed in the main body 20A of the multilayered wiring board so as to penetrate the inner layer, and the main body 20A undergone black color oxidation. The black color oxidation is performed by submerging the main body 20A into heated mixed liquid of potassium peroxide and caustic soda. Thus, a black oxide film 25 is formed on only exposed surfaces 22a and 23a of inner layers 22 and 23 made of copper. The main body 20B of the multilayered wiring board which has undergone the black color oxidation becomes an object for inspection, and the inspection is performed. Here, the inside of the hole 24 has the green color when a substrate 21 is made of glass epoxy and has a brown color when the substrate is made of glass polyimide. The black film 25 is visually recognized. Therefore, the constrast of the exposed surfaces 22a and 23a with respect to the substrate 21 becomes clear, and the inspection with regard to the deviation of the inner layer can be improved.