An oblique incidence interferometer has favorable measurement accuracy while achieving miniaturization. The oblique incidence interferometer includes a light source that emits coherent light; a beam dividing unit that divides the coherent light from the light source into a measurement beam and a reference beam, polarizing directions of both beams being perpendicular to each other; a first beam folding unit that folds the measurement beam divided by the beam dividing unit to cause the folded measurement beam to be incident on the measurement object surface at a predetermined angle relative to the measurement object surface; a second beam folding unit that folds the measurement beam reflected by the measurement object surface; and a beam combining unit that combines the measurement beam folded by the second beam folding unit with the reference beam.