In continuous radiography, while a patient stands in front of an imaging support, a total image capture field is determined. The total image capture field is divided into small image capture fields. A map scaling section scales up or down a full spine irradiation area map in accordance with the size of the total image capture field. A map dividing section divides the scaled map into small maps corresponding to the small image capture fields. In each division exposure, a detection pixel selector selects one or more detection pixels belonging to an irradiation area defined by the small map, out of all detection pixels distributed in an imaging surface of an electronic cassette. If an integration value of a detection signal from the selected detection pixel reaches a threshold value, X-ray emission is stopped. Division X-ray images obtained by the division exposures are merged into a single continuous X-ray image.
