An optical isolator comprises two birefringent plates one of which separates two light components whose planes of polarization are perpendicular to each other to make the two light components spatially separate between the two birefringent plates and pass through two separate optical paths and the other of which thereafter combines the two separate light components, two Faraday rotators disposed between the two birefringent plates and having a Faraday rotation angle of approximately 45 degrees, a polarizer disposed between the two Faraday rotators and having a predetermined polarized-light transmitting angle, and a magnetic field device for applying an external magnetic field to the two separate optical paths in the two Faraday rotators to magnetize respective regions near the two optical paths in each of the rotators in opposite magnetization directions to each other. In this arrangement two light components entering the polarizer in the forward direction has the same angle of plane of polarization as the predetermined polarized-light transmitting angle of the polarizer so as to pass through the polarizer, but two light components entering the polarizer in the reverse direction has an angle of plane of polarization perpendicular to the predetermined polarized-light transmitting angle of the polarizer so as not to pass through the polarizer. The high performance polarization-independent optical isolator may be obtained with high isolation of more than 50 dB, which is easy in assembling or manufacturing.