A projection type image display apparatus capable of achieving accurate focusing
of a projection optical system using an output from a photoreception sensor, is
disclosed. The projection type image display apparatus includes a projection optical
system and performs focusing control of the projection optical system based on
an output signal from an photoreception sensor. The photoreception sensor receives
light from the projection surface. The optical axis of the projection optical system
is shifted with respect to a reference axis. The reference axis leads from the
center of an original image formed on an image forming element to the center of
the projected image. The photoreception sensor receives light from a detection
area which is proximate to and includes the position of the optical axis of the
projection optical system on the projection surface.
