An optical switch includes at least one light-receiving core (a) for receiving an optical signal, a plurality of light-emitting cores (b, c) which are used selectively for emitting the optical signal, and a plurality of waveguides (1) connecting the light-receiving core and the plurality of light-emitting cores. A nonlinear optical element (3) which, when pumped, changes its refractive index by 2% or above relative to the surroundings to control a traveling direction of the optical signal is disposed near at least one of the plurality of waveguides.