In view of a specific area having a characteristic surface state in a
mark-formed area or a surrounding area thereof, an area calculation unit
has a window having a dimension corresponding to the specific area scan
the whole measurement area in order to obtain a quantity representing a
surface state based on measured signals through the window, and then, by
identifying a measured signal area corresponding to the specific area
based on the quantity as a function of the window's position, extracts a
measured signal area corresponding to the mark. And a position calculation
unit performs computation such as pattern-matching on the signal area
extracted, thereby detecting the position of the mark accurately and
quickly.
