To provide an optical isolator which facilitates an assembling work, especially, the work to set a Farady rotator into a magnet.

This optical isolator is provided with a first polarizer 3, a Farady rotator 4 provided adjacently to this first polarizer 3, a second polarizer 7 which is provided so as to face the first polarizer to the Farady rotator 4 between them, and an annular magnet 8 provided around the Farady rotator 4, and a first annular magnet partial body 2 and a second annular partial body 6 are combined to constitute the magnet 8.