An optical scanner for an image forming apparatus of the present invention
includes a polygonal mirror for steering a scanning beam incident thereto
and an optical device located in the vicinity of the polygonal mirror.
The polygonal mirror and optical device are supported by a housing. A
heat radiation guide adjoins the polygonal mirror and is formed
integrally with or separately from the housing. The heat radiation guide
has a guide surface inclined relative to the axis of rotation of the
polygonal mirror and intersecting a plane virtually formed by a scanning
beam.