There are provided the following components: an FPD that has a plurality of pixels, in which signal electric charges corresponding to amounts of X-rays incident are accumulated, and that is capable of nondestructively reading data which indicates the X-ray image; an amplifier that amplifies a signal sent from the FPD and has a variable gain; an evaluation value calculation section that obtains an evaluation value for evaluating the X-ray image; and a gain adjustment section that calculates a new gain of the amplifier used at the time of rereading. The gain of the amplifier is changed to a value of a new gain which is calculated by the gain adjustment section, and the X-ray image is reread.