A radiation imaging apparatus comprising: a plurality of pixels including a detection pixel, and a correction pixel whose sensitivity for radiation is lower than sensitivity of the detection pixel; and a decision means configured to execute a reset operation of resetting charges accumulated in the plurality of pixels and a decision operation of deciding a radiation dose during irradiation to the radiation imaging apparatus, wherein the decision means ends the reset operation and starts the decision operation before a start of radiation irradiation, and in the decision operation, the decision means reads out signals from the detection pixel and the correction pixel at least once before the start of radiation irradiation and after a predetermined time elapses since the end of the reset operation, and decides a first correction value based on the signal read out from the detection pixel and a second correction value based on the signal read out from the correction pixel, and reads out signals from the detection pixel and the correction pixel after receiving a radiation irradiation start request, and decides the radiation dose during irradiation to the radiation imaging apparatus by amending a value of the signal read out from the detection pixel based on a value of the signal read out from the correction pixel, the first correction value, and the second correction value. a plurality of pixels including a detection pixel, and a correction pixel whose sensitivity for radiation is lower than sensitivity of the detection pixel; and a decision means configured to execute a reset operation of resetting charges accumulated in the plurality of pixels and a decision operation of deciding a radiation dose during irradiation to the radiation imaging apparatus, wherein the decision means ends the reset operation and starts the decision operation before a start of radiation irradiation, and in the decision operation, the decision means reads out signals from the detection pixel and the correction pixel at least once before the start of radiation irradiation and after a predetermined time elapses since the end of the reset operation, and decides a first correction value based on the signal read out from the detection pixel and a second correction value based on the signal read out from the correction pixel, and reads out signals from the detection pixel and the correction pixel after receiving a radiation irradiation start request, and decides the radiation dose during irradiation to the radiation imaging apparatus by amending a value of the signal read out from the detection pixel based on a value of the signal read out from the correction pixel, the first correction value, and the second correction value. reads out signals from the detection pixel and the correction pixel at least once before the start of radiation irradiation and after a predetermined time elapses since the end of the reset operation, and decides a first correction value based on the signal read out from the detection pixel and a second correction value based on the signal read out from the correction pixel, and reads out signals from the detection pixel and the correction pixel after receiving a radiation irradiation start request, and decides the radiation dose during irradiation to the radiation imaging apparatus by amending a value of the signal read out from the detection pixel based on a value of the signal read out from the correction pixel, the first correction value, and the second correction value.