A radiation imaging apparatus includes a first pixel, and a second pixel whose sensitivity for radiation is lower than sensitivity of the first pixel; and a decision unit configured to execute a reset operation of resetting charges in the pixels and a decision operation of deciding a radiation dose during irradiation to the apparatus. In the decision operation, the decision unit reads out signals from the first and second pixels at least once, and decides first and second correction values based on the signal read out from the first and second pixel respectively, and reads out signals from the first and second pixels after receiving a radiation irradiation start request, and decides the radiation dose during irradiation to the apparatus using values of the signals read out from the first and second pixels and the first and second correction values.