A radiation imaging apparatus, comprising a plurality of sensors, a holding unit configured to hold a signal level of each sensor, a monitor unit configured to monitor the signal levels, and a control unit configured to control each sensor so as to detect radiation with a first sensitivity and a second sensitivity higher than the first sensitivity, wherein the control unit performs first control to cause the monitor unit to monitor signal levels with the second sensitivity, and performs second control to select some sensors out of the plurality of sensors based on monitoring results obtained in the first control.
