An imaging device is provided with: an imaging element (21) in which a high-sensitivity pixel group (22a) and a normal-sensitivity pixel group (22b) are arranged; a control unit (31) for reading onlythe high-sensitivity pixel group (22a) and forming a first frame signal, reading all pixels including the high-sensitivity pixel group (22a) and the normal-sensitivity pixel group (22b) and forming asecond frame signal, and outputting the first and second frame signals in alternating fashion; a drive control circuit (32) and a timing generating circuit (23); and a frame addition circuit (35) forperforming frame addition processing of the first and second frame signals and outputting the result as a single image signal.