A radiation imaging apparatus, comprising a plurality of sensors and a driving unit, each sensor including a detection element, a sampling unit and a reset unit, wherein the driving unit performs an operation of causing the reset unit to initialize the detection element, an operation of causing the sampling unit to sample a signal from the detection element in accordance with radiation irradiation started after the operation of initializing, and an operation of outputting a signal sampled by the operation of sampling, and wherein the driving unit changes, in accordance with a frame rate, a timing of the operation of outputting while maintaining constant a time from the operation of initializing to the operation of sampling.