PURPOSE: To obtain high productivity even if the area of a subject is wide by providing an imaging optical system with first and second roof reflectors having first and second reflection surfaces and third and fourth reflection surfaces and an imaging body.

CONSTITUTION: This imaging optical system is arranged between a subject surface gh and an imaging plane and is composed of the first roof reflector, the second roof reflector and an imaging lens. The first roof reflector has the two reflection surfaces inclined 45° with the subject surface gh and the imaging plane and the second roof reflector has the two reflection surfaces inclined 45° with the subject surface gh and the imaging plane. More specifically, the imaging optical system consists of a roof prism array 100 formed by arranging plural roof prisms parallel with the subject surface gh, a roof prism array 200 formed by arranging the plural roof prisms parallel with the subject surface gh and a lens array 300 formed by arranging plural lens blocks parallel with the subject surface gh.