A control apparatus of a radiation imaging apparatus configured to generate a plurality of radiation images to transmit to an external apparatus is provided. The control apparatus includes an acquisition unit configured to acquire a generation cycle of the plurality of radiation images, a partial readout time required for the radiation imaging apparatus to read out a region of interest in one radiation image of the plurality of radiation images, and a transmission time estimated to be required to transmit the one radiation image. The control apparatus also includes a determination unit configured to determine, based on the generation cycle, the partial readout time, and the transmission time, a time at which the radiation imaging apparatus starts transmission of the plurality of radiation images.