A correction image acquisition process includes: a first gain image acquisition process of reading a pixel signal from a pixel region irradiated with radiation in a state in which a subject is not placed to acquire a first gain image; a pre-irradiation image acquisition process of reading the pixel signal from the pixel region in a state in which the subject is not placed and the radiation is not emitted to acquire a pre-irradiation image; a discarding process of discarding charge accumulated in a pixel of the pixel region after a dose of radiation that saturates the charge is emitted in a state in which the subject is not placed; a post-irradiation image acquisition process of reading the pixel signal from the pixel region to acquire a post-irradiation image after the discarding process is performed; and a second gain image acquisition process of subtracting the pre-irradiation image from the post-irradiation image to acquire a second gain image.