An optical displacement meter includes: a spatial filter configured to extract light under measurement of a wavelength focused on a measurement target and to specify the wavelength of the light under measurement; a polarizer configured to divide the light collimated and caused to propagate in one direction into linearly polarized beams in two directions orthogonal to a propagating direction; a wavelength plate that allows passage of the linearly polarized beams to produce elliptically polarized light having a phase difference commensurate with a light wavelength; a polarized light separator configured to divide the elliptically polarized light into polarized light components in the two directions; and a computing circuit configured to perform computation of (A−B)/(A+B) by use of light quantity signals A and B, which respectively correspond to the two polarized light components.