In a preparation step, a frame (10), a concave spherical seat (15), a convex spherical seat (13), a rotation body (16), a rotating shaft (12), and a work holder (17) are assembled, a laser head (33) is attached to the convex spherical seat (13), and a light receiving unit (38) is attached to the work holder (17). In a rotation body centering step, an irradiation position of a laser beam (LB) with respect to a laser irradiation surface (41) is changed by rotating the rotation body (16) while allowing the laser irradiation surface (41) to be irradiated with the laser beam (LB) emitted from the laser head (33) and a trajectory of the irradiation position is checked.
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