A sample inclination measuring method rotates, by a predetermined angle with respect to an interferometer apparatus, a columnar member having a leading end face in a planar form while the columnar member is held by a clamping apparatus, detects a relative angle between a reference surface of the interferometer apparatus and the leading end face at each of two rotational positions, and measures the inclination of the axis of the columnar member by using a predetermined arithmetic expression according to thus detected two angles.