PURPOSE: To enable detecting the outer diameter positions and the positions of orientation flat parts of wafers having various kinds of dimensions, by moving a detecting means of the outer diameter position and the position of the orientation flat part of a wafer, according to the dimension of a wafer.

CONSTITUTION: A wafer outer diameter detecting unit 5 has a surface which is fixed so as to make a projector part 3 and a light receiving part 3 face to each other via a wafer 2 and is in parallel with the wafer surface, and a surface which is perpendicular to the surface and in parallel with the orientation flat direction (m). An orientation flat detecting unit 8 has a surface which is fixed so as to make a projector part 6 and a light receiving part 7 face to each other via the wafer 2 and in parallel with the wafer surface, and a surface which is perpendicular to the surface and the orientation flat direction (m). A detecting means which detects at least one out of the outer diameter position and the position of the orientation flat part 202 of the wafer 2 is made possible to move according to the dimension of the wafer 2. Thereby the outer diameter position and the position of the orientation flat part 202 of the wafer 2 can be detected, and positioning is enabled.