A radiation imaging apparatus that includes a plurality of sensors, a readout unit and a control unit, wherein the control unit performs a first control of reading out signals from sensors after radiation irradiation is started, and a second control of outputting a control signal to end the radiation irradiation when a calculated value calculated based on an output of the readout unit in the first control reaches a reference value, and the control unit, in the first control, reads out the signals from the sensors by changing a signal amplification ratio of the readout unit such that a value of an output of the readout unit is not saturated, and, in the second control, calculates the calculated value by accumulating the output of the readout unit in consideration of the signal amplification ratio.