Abstract: Arranged, with spacing, are 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. Between the first separating/combining birefringent element and the first optical-path controlling birefringent element, is arranged first polarization rotating means 14 for changing a polarization direction from an orthogonal to a parallel or from a parallel to an orthogonal. Also, between the second optical-path controlling birefringent element and the second separating/combining birefringent element, is arranged second polarization rotating means 17. The first and second optical-path controlling birefringent elements are oppositely arranged symmetric in optical axis about an arrangement center thereof, between which is arranged a ½-wavelength plate for rotating 90 degrees a polarization direction of a light on a central optical path, thereby structuring an optical circulator.