A radiation detector includes a detection unit, a detection control unit, an image analyzing unit and a determination unit. The detection unit detects radiographic image data by plural pixels that convert applied radiation into electrical signals and store the electrical signals. The detection control unit controls the detection unit so as to determine that radiation has been applied if a read value obtained by reading the electric signals stored in the plural pixels is equal to or greater than a threshold value, and acquire radiographic image data corresponding to radiation that has passed through a subject. The image analyzing unit performs an image analysis with respect to the radiographic image if the read value is equal to or greater than the threshold value. The determination unit determines based on the result of the image analysis whether or not the radiographic image has been detected at an intended timing.