This invention intends to provide an optical isolator which is independent of a polarizing surface of an incident light and prevents the polarizing surface from changing at the light outgoing side. The optical isolator is composed of: a first parallel plate-like double-refractive substance; a first Faraday rotator for rotating a polarizing surface; a second parallel-like double refractive substance; a second Faraday rotator for rotating the polarizing surface in the direction reverse to that by the first Faraday rotator; a third parallel plate-like double-refractive substance; and a permanent magnet for magnetizing the Faraday rotators. In this way, the isolator is provided with a pair of Faraday rotators for rotating the polarizing surface in the directions reverse to each other and thus the polarizing surface stays unchanged on the light incidence side and light outgoing side. <IMAGE>
