1. An imaging apparatus comprising, in order from an object side: a scanning mirror; an optical system which has a flat shape; a two-dimensional image sensor which has a flat shape; and image composition processing means for connecting individual images scanned by the scanning mirror and obtained by the two-dimensional image sensor into one composite image, wherein the optical system coincides in direction of flatness with the two-dimensional image sensor, and wherein an aspect ratio α of an imaging surface of the two-dimensional image sensor satisfies the following condition: 
 0.05<α<0.5.