Abstract: An illumination correction apparatus for correcting a radiation beam incident on a reticle from an exposure apparatus includes a plurality of fingers each having a surface facing an incident direction of the radiation beam, the plurality of fingers being arranged in a first direction to be adjacent to a path of the radiation beam, and configured to adjust an amount of the incident radiation beam by moving in a second direction, intersecting the first direction, a controller connected to the plurality of fingers and configured to control movement of the plurality of fingers such that an intensity of the radiation beam has uniformity in the first direction, at least one optical sensor on the surface of at least one finger of the plurality of fingers, and a measurement unit configured to measure, based on an output of the at least one optical sensor, the intensity of the radiation beam.