An electronic cassette in a radiographic image capturing system includes a radiation detector for detecting radiation applied from an image capturing apparatus and transmitted through a patient, a contactless power receiver for receiving electric power supplied contactlessly from a power feeder and supplying the electric power to a battery, an A/D converter for performing an A/D conversion to convert analog radiographic image information generated based on the radiation applied to the radiation detector into digital radiographic image information, an end-of-A/D-conversion determining unit for determining whether the A/D conversion is finished or not, and a charging controller for stopping the power feeder from supplying electric power contactlessly after the image capturing apparatus has started capturing images until the end-of-A/D-conversion determining unit judges that the A/D conversion is finished.