Abstract: A radiation detection apparatus and a radiation image capturing system according to the present invention includes an electronic cassette equipped with a casing, and a radiation detection device accommodated inside the casing, which detects radiation emitted from a radiation source and having passed through a subject, while converting the radiation into radiation image information. The electronic cassette includes a sensor for sensing that the casing has been lifted, a power supply controller for supplying power based on a detection signal from the sensor, a discriminating unit for discriminating whether the radiation detection apparatus has transitioned to an image capturing capable mode, and a warning signal output unit for outputting a warning signal, for issuing a warning when the radiation detection apparatus cannot transition to the image capturing capable mode.