An imaging apparatus comprises a detecting unit for converting radiation or light into an electric signal provided with a plurality of pixels arranged in a matrix, each of the pixels including a conversion element and a switching element, a drive circuit unit for controlling a conducting state of the switching element, and a control circuit unit for controlling the drive circuit unit based on the electric signal converted by the detecting unit. The control circuit unit controls the drive circuit unit to perform steps including the drive circuit unit setting the switching elements at the conducting state row by row to acquire an offset image based on the signal accumulated in the plurality of pixels for subtraction processing of the image.