To provide a technique for accurately deciding the radiation dose during irradiation while shortening the time necessary until radiation irradiation becomes possible.SOLUTION: A radiation imaging apparatus comprises a plurality of pixels including a first pixel and a second pixel having sensitivity for radiation lower than that of the first pixel, and an exposure decision unit configured to execute a reset operation of resetting charges accumulated in the plurality of pixels and decision operation for deciding the radiation dose during irradiation to the imaging apparatus. The exposure decision unit, before irradiation of the radiation, completes the reset operation, starts the decision operation, and in the decision operation, reads signals from the first pixel and the second pixel one or more times, decides a first correction value on the basis of the signal read from the first pixel and a second correction value on the basis of the signal read from the second pixel, reads the signal from the first pixel and the second pixel after receiving a request to start irradiation of the radiation, and decides the radiation dose during irradiation to imaging apparatus, using the value of the signal read from the first pixel, the value of the signal read from the second pixel, the first correction value, and the second correction value.SELECTED DRAWING: Figure 6【課題】放射線照射が可能となるまでの時間を短縮しつつ、照射中の放射線量を精度よく決定するための技術を提供する。【解決手段】放射線撮像装置は、第１画素と、第１画素よりも放射線に対する感度が低い第２画素とを含む複数の画素と、複数の画素に蓄積した電荷をリセットするリセット動作と、放射線撮像装置に照射中の放射線の量を決定する決定動作とを実行するように構成された露出決定部とを備える。露出決定部は、放射線の照射開始前に、リセット動作を終了し、決定動作を開始し、決定動作において、第１画素及び第２画素から信号を１回以上読み出し、第１画素から読み出された信号に基づく第１補正値と、第２画素から読み出された信号に基づく第２補正値とを決定し、放射線の照射開始の要求を受信した後に、第１画素及び第２画素から信号を読み出し、第１画素から読み出された信号の値と、第２画素から読み出された信号の値と、第１補正値と、第２補正値とを用いて、放射線撮像装置に照射中の放射線の量を決定する。【選択図】図６
