To provide an interferometer which can instantly clear a moire fringe.

Plural light fluxes mutually different in a wave length are respectively divided into two parts, and are introduced to a measuring surface 10 and a reference surface 11, and the light fluxes from the measuring surface 10 and the reference surface 11 are made to interfere with each other, and interference fringes with every plural wave lengths are formed, and the plural interference fringes are superimposed on each other, and a synthetic interference fringe having a moire fringe is formed, and a bias component of light intensity is removed from the light intensity distribution of the synthetic interference fringe, or light intensity of the synthetic interference fringe is divided into two parts, and a phase of one light intensity of being divided into two parts is reversed, and a difference from the other light intensity is found, and afterwards, a minus component is converted into a plus component, and density of the synthetic interference fringe is doubled.