A reflective mask includes a central region and first and second peripheral regions at opposite sides of the central region, respectively, the first peripheral region including a first out-of-band region having a first edge region extending in a first direction, and a first expansion region between the first edge region and the central region, and a first outer auxiliary region adjacent to the first expansion region of the first out-of-band region in the first direction, the first outer auxiliary region having a first auxiliary pattern region.