PURPOSE: To provide the optical circulator which functions as an optical branching and coupling device suitable for optical fiber communication, etc., by using optical parts as parallel flat plates and using a magneto-optical crystal plate and optically rotatory crystal.

CONSTITUTION: This optical circulator has composite polarizing elements 21 to 24 having a pair of the parallel flat plates double refractive crystals and is arranged with the magneto- optical crystal 4 and the optically rotatory crystal 3 between the elements 22 and 23. Further, a permanent magnet 5 is disposed in the crystal 4. The composite polarizing elements 21 to 24 are formed by sticking a pair of the parallel flat plates double refractive crystals (for example, 11 and 12) which are diametrically opposite in the respective optical axis directions to each other. The respective elements have the same length. The respective crystals 11 to 18 split randomly polarized light to two orthogonally intersecting polarized luminous fluxes of ordinary light and extraordinary light. As a result, the optical circulator is easily assembled by using large plates of the double refractive crystals having good characteristics. Further, the optical separating and coupling device which depend on combination of the double refractive crystals 11 to 18 and the optically rotatory crystal 3, do not depend on polarization and have a good degree of separating and coupling is obtd. in such a manner that the errors in the assembly accuracy lessen the influence on the degradation of performance.