PURPOSE: To discriminate the orientation of a plate-like body by visual observation in the succeeding process without particularly increasing the manufacturing cost for realization.

CONSTITUTION: There are provided first and second marks M1, M2, formed on a plate like body and a third mark M3 which is positioned not on the line for connecting the first to the second marks, but in the vicinity of the first or the second mark, and used for discriminating the direction of the plate-like body. The positions of the first and the third marks are detected by means of a first position detector, the position of the second mark is detected by means of a second position detector, and hence the orientation of the plate-like body is discriminated.