The invention intends to be able to perform a gain correction fully adequately. Hence, at the time of radiographing an object, a gain correction of the object image is performed based on a gain correction image (XRc1) derived by performing a light reset. On the other hand, at the time of radiographing an object, when a light reset is not performed, a gain correction of the object image is performed based on a gain correction image (XRc2) derived without performing the light reset.