PURPOSE: To obtain an optical switch which is constituted in the middle of an optical fiber by eliminating the need to expose a core material.

CONSTITUTION: An optical fiber 1 is crooked at four positions with radii r1, r2, r3, and r4 and in a case 3, upper and lower light absorbing materials 4 and 5 are arranged. The upper light absorbing material 4 is stuck on the reverse surface of a push button 6, which abuts on the collar 3a of the case by being thrusted invariably by a return spring 7. Consequently the upper and lower materials 4 and 5 do not contact with the crooked optical fiber 1 normally. When the push button 6 is pressed as shown in Fig. (c) to bring the materials 4 and 5 into contact with the upper and lower crooked parts of the optical fiber 1, the crooked parts vary in critical angle of reflection to absorb part of light entered from the left end by the material 4 and 5, and consequently greatly attenuated light appears at the right end. At the right end of the optical fiber 1, a photoelectric transducer such as a phototransistor is provided and the light is converted into an electric signal, performing various kinds of on-off control.