An optical isolator having a constitution in which a Faraday rotator is sandwiched by two polarizers, which can be more easily produced at a reduced cost. An optical isolator is constituted so that it comprises the following constituent elements in the described order: a first reflection-type polarizer made of a polymeric multilayer film; a Faraday rotator capable of rotating the polarizing. plane by 45 degrees; a tapered glass plate; and a second reflection-type polarizer made of a polymeric multi-layer film.