A radiation imaging apparatus that includes a plurality of sensors and a control unit, wherein the control unit performs a first control of monitoring, after a radiation irradiation is started, a signal of a first sensor and accumulating the monitored signal of the first sensor, a second control of outputting, in response to a calculated value obtained by the accumulation and reaching a target value, a control signal to end the radiation irradiation, and a third control of reading out, after the radiation irradiation is ended, the signals of the respective plurality of sensors, and the control unit changes a monitoring cycle of the first control based on the target value and an elapsed time since the radiation irradiation has been started.