An apparatus includes a detection unit including a plurality of two-dimensionally arranged pixels with a plurality of lines located between adjacent pixels, configured to detect an incident radiation and output signals related to a radiation image, a calculation unit configured to calculate a crosstalk ratio related to crosstalk occurring between the adjacent pixels with the plurality of lines therebetween in the detection unit, and a correction unit configured to make a correction to pixel data on a pixel affected by the crosstalk among a plurality of pieces of pixel data constituting the radiation image based on the crosstalk ratio.