A direction determination processor outputs imaging direction information representing the direction of an electronic cassette with respect to a subject during imaging of the subject. An image direction judging unit generates image direction information representing the direction of image data with respect to a reading direction in which a radiation detector is read, based on the imaging direction information, or based on the imaging direction information, imaging order information and a template. An image displaying direction determining unit generates displaying direction information, which represents a displaying direction of the image data on a display screen or a display device.