Alignment method

An alignment method for aligning an orientation flat that is formed on a circular workpiece having a first surface and a second surface opposite the first surface and a peripheral surface extending from the first surface to the second surface at an outer edge of the workpiece, the orientation flat being formed on the peripheral surface with a direction parallel to a desired direction, the method comprising:

• a positioning step of positioning an imaging unit, which images the workpiece, at a position where the orientation flat is able to be imaged;
• a straight-line detection step of imaging the orientation flat by the imaging unit to acquire a captured image and detecting a straight-line segment in the captured image;
• a first alignment step of calculating an off-angle between an extending direction of the straight-line segment detected in the straight-line detection step and the desired direction, and, on a basis of the off-angle, positioning the orientation flat such that the extending direction of the straight-line segment extends parallel to the desired direction;
• and
• a second alignment step of, after performing the first alignment step, imaging the orientation flat at a first position and a second position, which are spaced apart from each other along the desired direction, and positioning the orientation flat such that a line that connects together the orientation flat at the first position and the orientation flat at the second position extends parallel to the desired direction.