An imaging system includes a detector (104) having a first area where irradiation occurs in a radiation field (A) and a second area other than the first area where irradiation occurs in a radiation field (B) and configured to output image data, and an image processing unit (601) that performs image processing on the image data. The image processing unit (601) includes a storage unit (602) that stores dark output information, a measurement unit (607) that measures the integral dose of the radiation or light applied to a pixel in the first area and the integral dose of the radiation or light applied to a pixel in the second area, and a correction unit (610) that corrects the image data, based on the dark output information obtained from the storage unit (602) and the integral doses measured by the measurement unit (607), when changing of the radiation field has occurred.