A polarized wave coupling optical isolator comprises a plane-parallel birefringent element for optical path control, which is provided to control an optical path according to a polarizing direction, a plane-parallel birefringent element for coupling and splitting, which is provided with a certain interval from the birefringent element for optical path control to couple lights of different optical paths having polarizing directions set orthogonal to each other, and to split lights of the same optical path, a nonreciprocal portion provided between the birefringent element for optical path control and the birefringent element for coupling and splitting, and constructed by including a combination of 45° Faraday rotator and a linear phasor for rotating a plane of polarization by 45°, two input ports installed on the birefringent element side for optical path control, and an output port installed on the birefringent element side for coupling and splitting.