Abstract: The calibration method includes changing the emission direction of the measurement light to be emitted from the optical rotation probe by a minute angle from a reference direction set in advance, acquiring a shape error for a reference object after changing the emission direction by emitting the measurement light from the optical rotation probe toward the reference object while rotating the emission direction of the measurement light around an S axis and varying a relative position between the optical rotation probe and the reference object, and calculating an adjustment error of the emission direction of the measurement light with respect to the reference direction based on a theoretical value of the shape error for the reference object to be obtained in a case where the emission direction of the measurement light matches the reference direction and a measurement value of the acquired shape error for the reference object.