Patent ID: 7385733

Claim:
An imaging optical system for imaging information on an object surface in a region having a length (A) in a long side direction and a length (B) in a short side direction which satisfy a relation of A/B>10, on an image plane, comprising: a diaphragm; a first set of a plurality of off-axial reflection surfaces arranged on the object surface side from the diaphragm; and a second set of a plurality of off-axial reflection surfaces arranged on the image plane side from the diaphragm, wherein an optical path of a light beam passing through a center of the diaphragm and a center of the image plane is deflected by the off-axial reflection surfaces within a surface perpendicular to the long side direction of the region to undergo crossing at least once, wherein all of the off-axial reflection surfaces satisfy a conditional expression: |P|S<0.5 where P (mm −1 ) represents an optical power of the off-axial reflection surface within the surface perpendicular to the long side direction and S (mm) represents a distance from the off-axial reflection surface to a subsequent one of the off-axial reflection surfaces along a reference axis.