Patent ID: 8405757

Claim:
An imaging device comprising: a light source that emits light; a prism having an imaging surface to be contacted with an object having a pattern formed thereon so that the light from the light source totally reflects on the imaging surface; and an image-forming optical system that forms an image of the object, wherein said image-forming optical system comprises: a front lens group having a first optical axis tilted relative to the imaging surface, said front lens group having positive refractive power; an image plane tilted from a surface perpendicular to the first optical axis of the front lens group; and a rear lens group disposed on a side of the image plane relative to the front lens group and having a second optical axis shifted in parallel to the first optical axis of the front lens group, said rear lens group having negative refractive power, and said image-forming optical system is arranged to satisfy the following conditional expression: | Aim |/(90 °−Ain )<0.5 where Ain is an acute angle between the imaging surface and the first optical axis of the front lens group, and Aim is an angle between the image plane and a surface perpendicular to the first optical axis of the front lens group.