The optical system having an imaging lens that images a first-plane and a second-plane which are discontinuous includes: a first-optical-system that images the first-plane; a second-optical-system that images the second-plane; and a common-optical-system that forms a subject image, which is incident through the first-optical-system, on the first-light-receiving-region of the image sensor and forms a subject image, which is incident through the second-optical-system, on the second-light-receiving-region of the image sensor. In the optical system, an angle of view, at which imaging is performed by the first-optical-system and the common-optical-system, overlaps with an angle of view, at which imaging is performed by the second-optical-system and the common-optical-system. The optical system includes a first focus adjustment unit that adjusts the focus of the optical system composed of the first-optical-system and the common-optical-system and a second focus adjustment unit that adjusts the focus of the optical system composed of the second-optical-system and the common-optical-system.