The present invention provides a technique advantageous in suitably determining the irradiation end timing in a radiation imaging apparatus that can perform AEC.The radiation imaging apparatus comprises a sensor configured to detect radiation and a control unit, wherein the control unit generates, after the start of radiation irradiation, an evaluation value indicating the stability of a radiation irradiation intensity based on a sensor signal from the sensor, and the control unit outputs, in response to the evaluation value satisfying a predetermined condition, a signal indicating that the radiation irradiation intensity has stabilized.
