To provide an optical switch for redundancy furnished with a self diagnosis function.

The optical switch for redundancy is provided with: a set of arranged optical fibers 44 and another set of arranged optical fibers 46 which are arranged facing to each other; and at least an optical fiber 35 for spare circuit which can replace any one of optical fibers of the set optical fibers 44. A prism 32 is movable by a voice coil motor 29 and freely inserted into and retracted from the optical path between the certain optical fibers 44 and 46 facing to each other with an actuator 33. The prism 32 is projected into the optical path between the certain optical fibers 44 and 46, and connects the certain optical fiber 46 and the optical fiber 35 for spare circuit. In a self diagnosis time, the prism 32 is moved from the center to the outside of the end optical fiber with the voice coil motor 29, and the time required for the movement is measured, thus, the existence/non-existence of troubles of the optical switch 21 for redundancy is decided on the basis of the time required for the movement.

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