An optical switch in which the adverse effect of heating can be restrained is realized. An optical switch for switching a transmission path of an optical signal by a change in refractive index due to carrier injection comprises: a semiconductor substrate; an optical waveguide layer which is formed on the semiconductor substrate and in which an optical waveguide is formed, the optical signal being incident on the optical waveguide from one side, then branched into two at a halfway part and emitted from the optical waveguide; a first electrode formed on the optical waveguide layer and at a branching part of the optical waveguide; a second electrode formed on the optical waveguide layer and near the branching part of the optical waveguide; and a third electrode formed on the optical waveguide layer and on a side opposite to the first electrode as viewed from the second electrode; wherein when the optical switch is on, carriers are injected from the first and second electrodes, and when the optical switch is off, carriers are injected from the second and third electrodes.