An interferometric optical device that measures the curved wall shape of a cylindrical object and includes: an interferometric optical system that emits measurement light at the curved wall of the object, collects the light reflected by the object, and creates a composite wave that combines the reflected light and a reference light; a rotation drive assembly that is connected to the interferometric optical system and rotationally displaces the interferometric optical system centered about a rotation axis that coincides with a center axis of the cylindrical shape of the object; a sensor that acquires a two-dimensional distribution of the intensity of the composite wave using a plurality of photoreceptor elements arrayed two-dimensionally; and a computation device that computes the internal wall shape of the object based on the plurality of two-dimensional distributions acquired in a state where a rotation angle for the rotation drive mechanism varies.