A stage apparatus has a substrate holding unit which chucks and holds a substrate, and includes a flat surface having a recess where the substrate holding unit is to be mounted. A fixing member fixes a projection support provided to the substrate holding unit onto the flat surface. The substrate holding unit is supported by the fixing member while a distal end of the projection support is in contact with the recess of the flat surface and the remaining portion of the substrate holding unit is not in contact with the flat surface.