An imaging device includes a housing including first and second photographing apertures which are open toward opposite directions; an image pickup device provided in the housing; a main optical system forming incident light from the first photographing aperture onto an imaging surface of the image pickup device; and an insertable optical element movable between an insertion position in an optical path of a main optical system and a removed position out of the optical path of the main optical system, the insertable optical element constituting at least a part of a sub-optical system which forms incident light from the second photographing aperture onto the imaging surface when at the insertion position. When the insertable optical element is positioned in the insertion position, the sub-optical axis is offset from the main optical axis toward the removed position of the insertable optical element in the inserting/removing direction.