A radiation imaging apparatus comprising: a plurality of sensors (s) each including a detection element configured to detect radiation, a sampling unit (U SHS, U SHN) configured to sample a signal from the detection element, and a reset unit configured to initialize the detection element; and a driving unit configured to drive the plurality of sensors, wherein the driving unit is adapted to perform: a first reset (RD(k)) of causing the reset unit to initialize the detection element; a first sampling (SD(k)) of causing the sampling unit to sample a signal from the detection element in accordance with first irradiation started after the first reset (RD(k)); a first output (RO(k)) of outputting the signal sampled by the first sampling (SD(k)); a second reset (RD(k+1)) of causing the reset unit to initialize the detection element; a second sampling (SD(k+1)) of causing the sampling unit to sample a signal from the detection element in accordance with second irradiation started after the second reset (RD(k+1)) following the first irradiation; and a second output (RO(k+1)) of outputting the signal sampled by the second sampling (SD(k+1)), characterized in that the driving unit is adapted to start the first output (RO(k)) after completion of the second reset (RD(k+1)) and before the second sampling (SD(k+1)), and to change, in accordance with a frame rate, a timing of the first output (RO(k)), while maintaining constant a time from the first reset (RD(k)) to the first sampling (SD(k)) and a time from the second reset (RD(k+1)) to the second sampling (SD(k+1)). a plurality of sensors (s) each including a detection element configured to detect radiation, a sampling unit (U SHS, U SHN) configured to sample a signal from the detection element, and a reset unit configured to initialize the detection element; and a driving unit configured to drive the plurality of sensors, wherein the driving unit is adapted to perform: a first reset (RD(k)) of causing the reset unit to initialize the detection element; a first sampling (SD(k)) of causing the sampling unit to sample a signal from the detection element in accordance with first irradiation started after the first reset (RD(k)); a first output (RO(k)) of outputting the signal sampled by the first sampling (SD(k)); a second reset (RD(k+1)) of causing the reset unit to initialize the detection element; a second sampling (SD(k+1)) of causing the sampling unit to sample a signal from the detection element in accordance with second irradiation started after the second reset (RD(k+1)) following the first irradiation; and a second output (RO(k+1)) of outputting the signal sampled by the second sampling (SD(k+1)), a first reset (RD(k)) of causing the reset unit to initialize the detection element; a first sampling (SD(k)) of causing the sampling unit to sample a signal from the detection element in accordance with first irradiation started after the first reset (RD(k)); a first output (RO(k)) of outputting the signal sampled by the first sampling (SD(k)); a second reset (RD(k+1)) of causing the reset unit to initialize the detection element; a second sampling (SD(k+1)) of causing the sampling unit to sample a signal from the detection element in accordance with second irradiation started after the second reset (RD(k+1)) following the first irradiation; and a second output (RO(k+1)) of outputting the signal sampled by the second sampling (SD(k+1)), characterized in that the driving unit is adapted to start the first output (RO(k)) after completion of the second reset (RD(k+1)) and before the second sampling (SD(k+1)), and to change, in accordance with a frame rate, a timing of the first output (RO(k)), while maintaining constant a time from the first reset (RD(k)) to the first sampling (SD(k)) and a time from the second reset (RD(k+1)) to the second sampling (SD(k+1)).