1. An apparatus comprising: a plurality of imaging pixels configured to acquire a radiation image; a plurality of detection pixels each including a detection conversion element, which detects an incident radiation ray, and a detection switch element, which is connected to the detection conversion element; a drive unit configured to drive the detection switch element of each of the plurality of detection pixels; a plurality of detection regions in each of which the plurality of detection pixels are arranged; a control unit configured to control the drive unit to drive the plurality of detection pixels arranged in each of the plurality of detection regions at respective different timing; and an acquisition unit configured to acquire an amount of incidence of radiation rays on each of the plurality of detection regions based on a value obtained by summing or averaging signals read out from the plurality of detection pixels.