A diagnostic mat has a texture, which enables avoiding mismatching in diagnosis and calibration, such as uniform and unduplicated patterns, for example, random dot patterns, fractal, natural images, and the like. A robot apparatus placed on the diagnostic mat assumes a stance suitable for taking images of the diagnostic mat, creates a distance image from an image acquired by the stereo camera, and verifies the performance of the stereo camera based on the flatness of the diagnostic mat obtained from this distance image. This assists in diagnosing the offset of the stereo camera mounted on the robot apparatus due to the deterioration over time of the stereo camera, falling of the robot apparatus, and the like.