An imaging device that photographs a moving image, comprising: an imaging unit configured to repeatedly obtain image data of one frame in a first cycle, further divide a period of the one frame into periods of a predetermined number of divided frames, and repeatedly output divided image data for each divided frame; a gain application section configured to detect object luminance and apply a gain to a plurality of pieces of divided image data; and a synthesis processing section configured to combine the plurality of pieces of divided image data, to generate combined image data of one frame, wherein, when the plurality of pieces of divided image data is obtained in the imaging unit, the number of divided frames is not changed during the period of the first cycle, and wherein, when the number of divided frames is changed for a next cycle of the first cycle.