The present disclosure provides a radiation detection system, a radiation output device, and a radiation detection device. The radiation detection system includes a radiation output device having an output control unit, and a radiation detection device having a recognition unit that recognizes whether radiation has been output from the radiation output device on the basis of a radiation detection signal. The output control unit causes radiation to be output at a first intensity from a time point of the start of outputting of radiation, and then causes the radiation to be output at a second intensity. The first intensity is an intensity higher than the second intensity and satisfying a threshold value condition set in advance in the recognition unit. The recognition unit recognizes that a detection signal of the radiation with the first intensity satisfies the threshold value condition, thereby recognizing the start of outputting of the radiation.