An interferometer or an interference position measuring device is constituted
so that a low coherency light source (multi-mode semiconductor layer) or a plurality
of light sources with different wavelengths are used as a light source, a light
flux is split into two light fluxes in a light transmitting member, one light flux
(reference light flux) is emitted to a reference mirror fixed to an optical head,
and the other light flux is emitted to an object to be measured which moves or
displaces, the respective reflected light fluxes are multiplexed in the transmitting
member so that an interference light flux is obtained, a specified wavelength light
is extracted by a wavelength selecting filter through which only a specified wavelength
light transmits so as to be detected by a light receiving element.
