A radiation detecting cassette and a radiation image capturing system are provided. A radiation detecting cassette has a radiation detector for detecting a radiation having passed through a patient and converting the detected radiation into radiation image data, a transceiver for transmitting the radiation image data by way of wireless communications, a cassette controller for controlling the radiation detector and the transceiver, a power supply for energizing the radiation detector and the transceiver, and a remaining power supply power level detector for detecting a remaining power level RC [%] of the power supply. The cassette controller includes a data transmission and reception controller. The cassette controller stops transmitting the radiation image data by way of wireless communications and prioritizes the capturing of a radiation image when the detected remaining power level of the power supply is smaller than a predetermined threshold.