A reference sample (41) has a step/terrace structure made of monocrystalline SiC and a surface of each terrace has first or second stack orientation. In the reference sample (41), contrast as difference in lightness and darkness between an image of a terrace with a surface directly under which the first stack orientation lies and an image of a terrace with a surface directly under which the second stack orientation lies changes according to an incident electron angle which is an angle that an electron beam emitted from a scanning electron microscope forms with a perpendicular to the terrace surface. Even when a SiC substrate has an off angle (e.g., from 1° to 8°), using an inclined support base (20a) capable of correcting the off angle enables sharp contrast that reflects difference between the first and second stack orientations directly under the surface to be obtained irrespective of the off angle.