A two-port isolator includes a first center electrode and a second center electrode which are wound around a ferrite to which a direct-current magnetic field is applied from permanent magnets, and the ferrite is mounted on a circuit board having built-in matching circuit devices. The ferrite is preferably substantially rectangular-parallelepiped-shaped having first and second principal surfaces that are substantially parallel to each other, and the long-side length of the principal surfaces is about 1.5 to about 5 times the short-side length. The second center electrode is wound between one and four turns around the ferrite.