A mirror device may include: a mirror including a base plate, a reflective film on a first surface of the base plate, and a plurality of first protrusions on a second surface of the base plate; a plurality of support parts for respectively supporting the plurality of the first protrusions, each support part having a groove formed therein for guiding the first protrusion; and a plurality of clamps for respectively pressing the plurality of the first protrusions against the respective grooves in the plurality of the support parts.