In a light beam sensor (40) of a position adjuster, a light beam irradiated
from a cross dichroic prism (150) is directly received by a CCD camera (41)
via a beam splitter (451), so that the position adjuster can be adjusted
without using a conventional projection screen and great size reduction of the
position adjuster is possible, and, since only small space is required for installing
the position adjuster, workspace can be efficiently utilized.
