PROBLEM TO BE SOLVED: To achieve both readiness and accuracy in irradiation start determination.SOLUTION: An electronic cassette 13 includes a panel part 35 in which pixels 41 for accumulating signal charges indicating image signals by receiving an X-ray are two-dimensionally arranged. The panel part 35 includes a detection pixel 41b which detects the X-ray. A signal processing circuit 47 periodically samples dose signals in accordance with the dose per unit time of the X-ray from the detection pixel 41b. An irradiation start determination part 58 performs primary determination processing for determining whether or not the irradiation of the X-ray is started on the basis of the dose signal and secondary determination processing for determining whether or not the primary determination result is correct. A control part 48 sets a sampling period SP2 in the secondary determination processing to be longer than a sampling period SP1 in the primary determination processing.SELECTED DRAWING: Figure 9
