The present invention includes a preparatory step of providing a calibration work piece having a flat reflecting surface as a work piece, and arranging the reflecting surface to be parallel to a standard optical axis and orthogonal or parallel to pixel array directions of an image capture element; a rotation step of rotating a prism centered on the standard optical axis; a brightness detection step of detecting the brightness of an image captured by the image capture element at each of a plurality of rotation positions of the prism; and a positioning step of aligning the prism at a rotation position where the brightness detected by the brightness detection step is greatest.