PROBLEM TO BE SOLVED: To easily supply power to a radiation detecting device and to acquire a radiation image of high quality.SOLUTION: An electronic cassette 24 mounted to a radiation image capturing system 10 comprises: a radiation detecting device 40 for detecting radiation X emitted from an image capturing apparatus 22 and transmitted through a patient 14； a contactless power reception part 49 for receiving electric power supplied by non-contact from a power feeder 25 and supplying the electric power to a battery 44； an A/D converter 70 for performing A/D conversion to convert radiation image information generated due to the radiation X applied to the radiation detecting device 40； an end-of-A/D conversion determining part 107 for determining whether the A/D conversion is finished； and a charging controller 108 for stopping the power feeder 25 from supplying electric power by non-contact after the image capturing apparatus 22 has started capturing images until the end-of-A/D conversion determining part 107 determines that the A/D conversion is finished.
