An AEC unit of an electronic cassette sets a dose target value and a short-circuited pixel used for AEC based on a radiographing condition. When a control unit of the electronic cassette detects start of irradiation of X rays, the AEC unit starts integration of a cumulative dose of X rays which are incident to a target region based on a dose detection signal output by the short-circuited pixel. The AEC unit predicts a stop timing at the time point t1, waits until the time point t2 which is a predetermined time earlier than a scheduled stop time, and sends a stop timing notification to an X-ray generation device at the time point t2. When the stop timing notification is received, a X-ray source control device immediately inputs an irradiation stop command so as to stop an operation of an X-ray source.