An imaging apparatus has an AEC function that can prevent irregularities in photographed images, without being increased in size. The imaging apparatus comprises a plurality of pixels arranged in a matrix shape, each of the plurality of pixels including a conversion element for converting radiation or light into an electric charge, a plurality of lines that are connected to the plurality of pixel units and that extend in different directions to each other, a current monitor circuit that monitors currents flowing in the plurality of lines, and an arithmetic unit that calculates a two-dimensional distribution by performing back-projection processing with respect to the currents flowing in the plurality of lines monitored by the current monitor circuit.