PROBLEM TO BE SOLVED: To speedily perform processing based on an output of a radiation dose detecting sensor.SOLUTION: An FPD35 includes a pixel 36 for image detection and a detection pixel 65 for radiation dose detection. A signal processing circuit 43 is a pipeline type which is provided with first and second buffer memories 54a and 54b at a post stage of an A/D converter 53. During radiation dose detecting operation, the signal processing circuit 43 performs, in a first cycle, inputting of a radiation dose detecting signal Sd, which is based on electrical charge s from the detection pixel 65, into the first buffer memory 54a, and outputting of a dummy signal Dd from the second buffer memory 54b, in parallel. In a second cycle, which is shorter than the first cycle, the outputting of the radiation dose detecting signal Sd from the first buffer memory 54a, and the inputting of the dummy signal Dd into the second buffer memory 54b are performed in parallel. The first cycle and the second cycle are alternately repeated, and an irradiation start of X-radiation is detected with an irradiation start detector 61 by use of the radiation dose detecting signal Sd.
