PURPOSE: To select three kinds of wavelength by using many stages of optical filters and beam splitters to take out a P-polarized light in a three-wavelength area.

CONSTITUTION: An incidence light in the wavelength area of wavelengths λ1, λ2, λ3, λ4, λ5, and λ6 (λ1>λ2≥λ3≥λ4≥λ5>λ6) is made incident on an optical filter 1 which intercepts ≥90% of the light having a wavelength longer than λ1 and permits >80% of the light having a wavelength shorter than λ1 to pass through. The light transmitted through the filter 1 is converted to a P-polarized band light having a wavelength λ1Wλ2 by a narrow band polarizing beam splitter 2 which is operated with the wavelength λ1Wλ2 and reflects ≥95% of the light having a wavelength shorter than λ2, and this P-polarized band light passes a mirror 7 for wavelength λ1Wλ2 and is made incident on an optical switch where a liquid crystal is sealed. A P-polarized band light having a wavelength λ3Wλ4 and that having a wavelength λ5Wλ6 are formed similarly by combination of optical filters, beam splitter, etc., and are made incident on a driving part 8, and thus, a three-wavelength selecting type liquid crystal switch of high reliability is obtained which has a high light transmittance even for a short wavelength light area and has a wide applicability and does not require narrow band filters and upon which the influence of change in the lapse of time is little.