A comparison circuit 78 of an AEC unit 67 of an electronic cassette 13 compares the accumulated value of a detection signal from a detection pixel 65 of the electronic cassette 13 with an irradiation prohibition threshold value on the electronic cassette 13. When the accumulated value of the detection signal reaches the irradiation prohibition threshold value on the electronic cassette 13, a detection signal having the same voltage value as the irradiation prohibition threshold value of the radiographing condition on the source control device 11 paired with the radiographing condition on the electronic cassette 13 is output from a detection signal I/F 80 of the electronic cassette 13 toward a detection signal I/F 26 of the source control device 11.
