An anomaly in a high-pressure fuel system of an internal combustion engine is diagnosed early on and with high precision, and, further, the anomaly site is identified. A portion of an outer wall of the case member is formed by the passage wall, and a recess is provided in the outer wall of the case member with a portion of the passage wall facing the recess. The program calculates the dot products between the subsurface normals. Bumps are formed over the conductive protrusions and conductive pillars.