A radiation imaging apparatus comprising: a pixel array including a plurality of pixels; and a readout circuit configured to read out a signal from the pixel array, each of the plurality of pixels including: a conversion element configured to convert a radiation into an electrical signal; and a first sample-and-hold circuit configured to perform sampling-and-holding a plurality of times on a signal from the conversion element in response to the radiation, wherein the radiation imaging apparatus further comprises: a processing unit configured to perform, based on information about temporal change in radiation energy of the radiation obtained based on signals on which the sampling-and-holding has been performed the plurality of times by the first sample-and-hold circuit and read out non-destructively the plurality of times by the readout circuit, processing of determining timings of a plurality of times of sampling-and-holdings, and a control unit configured to perform control so that at least one of the plurality of times of sampling-and-holdings is performed by a second sample-and-hold circuit at the timings determined by the processing unit, each of the plurality of pixels including the second sample-and-hold circuit. a pixel array including a plurality of pixels; and a readout circuit configured to read out a signal from the pixel array, each of the plurality of pixels including: a conversion element configured to convert a radiation into an electrical signal; and a first sample-and-hold circuit configured to perform sampling-and-holding a plurality of times on a signal from the conversion element in response to the radiation, a conversion element configured to convert a radiation into an electrical signal; and a first sample-and-hold circuit configured to perform sampling-and-holding a plurality of times on a signal from the conversion element in response to the radiation, wherein the radiation imaging apparatus further comprises: a processing unit configured to perform, based on information about temporal change in radiation energy of the radiation obtained based on signals on which the sampling-and-holding has been performed the plurality of times by the first sample-and-hold circuit and read out non-destructively the plurality of times by the readout circuit, processing of determining timings of a plurality of times of sampling-and-holdings, and a control unit configured to perform control so that at least one of the plurality of times of sampling-and-holdings is performed by a second sample-and-hold circuit at the timings determined by the processing unit, each of the plurality of pixels including the second sample-and-hold circuit. a processing unit configured to perform, based on information about temporal change in radiation energy of the radiation obtained based on signals on which the sampling-and-holding has been performed the plurality of times by the first sample-and-hold circuit and read out non-destructively the plurality of times by the readout circuit, processing of determining timings of a plurality of times of sampling-and-holdings, and a control unit configured to perform control so that at least one of the plurality of times of sampling-and-holdings is performed by a second sample-and-hold circuit at the timings determined by the processing unit, each of the plurality of pixels including the second sample-and-hold circuit.