An optical device (1a-1f) including a Faraday rotator, wherein the Faraday rotator includes a Faraday element made of a magnetooptical material, two plate-shaped permanent magnets, and an electromagnet, wherein, with a direction of travel of light as a front-rear direction, the Faraday element includes light incident/emission surfaces at the front and rear, and surfaces parallel to each other to the left and right, wherein the two plate-shaped permanent magnets are attached respectively to the left and right side surfaces of the Faraday element such that different magnetic poles are opposed to each other, the permanent magnets being configured to apply a permanent magnetic field to the Faraday element in the left direction or the right direction, and wherein the electromagnet is configured including a coil made by winding a conductor around a periphery of the Faraday element to apply variable magnetic field in the front-rear direction, characterized: by a shaft part that holds the Faraday element, attached with the plate-shaped permanent magnets, over the entire length in the front-rear direction; in that the coil made by winding a conductor around a periphery of the shaft part with the front-rear direction as an axis; in that a front end and a rear end of the shaft part protrude further respectively to the front and the rear than do a front end and a rear end of the coil; and by a support base that supports the protruding sections of the shaft part from below. a Faraday element made of a magnetooptical material, two plate-shaped permanent magnets, and an electromagnet, wherein, with a direction of travel of light as a front-rear direction, the Faraday element includes light incident/emission surfaces at the front and rear, and surfaces parallel to each other to the left and right, wherein the two plate-shaped permanent magnets are attached respectively to the left and right side surfaces of the Faraday element such that different magnetic poles are opposed to each other, the permanent magnets being configured to apply a permanent magnetic field to the Faraday element in the left direction or the right direction, and wherein the electromagnet is configured including a coil made by winding a conductor around a periphery of the Faraday element to apply variable magnetic field in the front-rear direction, characterized: by a shaft part that holds the Faraday element, attached with the plate-shaped permanent magnets, over the entire length in the front-rear direction; in that the coil made by winding a conductor around a periphery of the shaft part with the front-rear direction as an axis; in that a front end and a rear end of the shaft part protrude further respectively to the front and the rear than do a front end and a rear end of the coil; and by a support base that supports the protruding sections of the shaft part from below. and wherein the electromagnet is configured including a coil made by winding a conductor around a periphery of the Faraday element to apply variable magnetic field in the front-rear direction, characterized: by a shaft part that holds the Faraday element, attached with the plate-shaped permanent magnets, over the entire length in the front-rear direction; in that the coil made by winding a conductor around a periphery of the shaft part with the front-rear direction as an axis; in that a front end and a rear end of the shaft part protrude further respectively to the front and the rear than do a front end and a rear end of the coil; and by a support base that supports the protruding sections of the shaft part from below. by a shaft part that holds the Faraday element, attached with the plate-shaped permanent magnets, over the entire length in the front-rear direction; in that the coil made by winding a conductor around a periphery of the shaft part with the front-rear direction as an axis; in that a front end and a rear end of the shaft part protrude further respectively to the front and the rear than do a front end and a rear end of the coil; and by a support base that supports the protruding sections of the shaft part from below. in that a front end and a rear end of the shaft part protrude further respectively to the front and the rear than do a front end and a rear end of the coil; and by a support base that supports the protruding sections of the shaft part from below.