A first separating/combining birefringent element 10, first and second optical-path controlling birefringent elements 11, 12, and a second separating/combining birefringent element 13 are spaced apart. Between the first separating/combining birefringent element and the first optical-path controlling birefringent element, a first polarization rotating means 14 is arranged for changing a polarization direction from an orthogonal relationship to a parallel relationship, or from a parallel relationship to an orthogonal relationship. Also, between the second optical-path controlling birefringent element and the second separating/combining birefringent element, a second polarization rotating means 17 is arranged. The first and second optical-path controlling birefringent elements are oppositely arranged symmetrically on optical axis about an arrangement center thereof, between which is arranged a ½-wavelength plate for rotating a polarization direction of a light on a central optical path 90 degrees, thereby structuring an optical circulator. With a similar structure, an optical switch can be structured by using a ±45-degree variable Faraday rotator in the first and second polarization rotation switch means.