PURPOSE: To provide the optical switch which executes switching operation at a high speed and is small in size.

CONSTITUTION: This optical switch has an input side light transmission path 1 having an exit end face IA inclined at an angle α with an optical axis, an output side light transmission path 2 having an incident end face 2A orthogonal with the optical axis, a light source capable of varying the output for feeding light to the input side light transmission path 1 freely to various intensities and a condenser lens 5 aligned in the optical axis interposed between the input side light transmission path 1 and the output side light transmission path 2 to the optical axis of the output side light transmission path 2. The input side light transmission path 1 consists of a material having a nonlinear type electro- optic effect to attain a large refractive index n10 at the light intensity at a stationary time. The intersection angle δ of the optical axis of the input side light transmission path 1 and the optical axis of the output side light transmission path 2 satisfies a relation cosα/cos(δ+α)=n0/n10 when the refractive index of air is defined as n0.