A grazing incidence interferometer is configured to measure a profile of a target surface using a measurement beam radiated on the target surface in a direction oblique to a normal line of the target surface and reflected on the target surface to cause an interference with a reference beam. The grazing incidence interferometer includes: a light source to emit light; a first polarization beam splitter that splits the light from the light source into the reference beam and the measurement beam; a ratio changer that changes a light amount ratio between the reference beam and the measurement beam; a second polarization beam splitter that synthesizes the measurement beam reflected on the target surface and the reference beam; and an image capturing camera that receives the synthesized beam of the reference beam and the measurement beam.