The imaging device 1 has an image sensor 14 and an electronic diaphragm section. In the image sensor 14, a plurality of pixels having an organic layer for photoelectric conversion is two-dimensionally arranged. Each pixel of the image sensor 14 is divided into a plurality of regions. The pixel has an on-chip microlens 15, which forms a pupil image of a photography optical system 12 on the plurality of regions, and reading sections 16 which respectively read photoelectrically converted signals of the divided regions. The electronic diaphragm section electronically controls an aperture value, and selects divided regions, which are read by the reading sections 16, on the basis of the aperture value, or selects a signal from the signals of the plurality of divided regions, which are read by the reading sections 16, on the basis of the aperture value.