A first light reflection surface (51) and a second light reflection surface (52) are formed on a lower half of a mirror block (50) in a state that these light reflection surfaces (51), (52) make 90 degrees therebetween. A first light reflection surface (51) and a second light reflection surface (52) are also formed on an upper half of the mirror block (50) in a state that these light reflection surfaces (51), (52) make 90 degrees therebetween. A third light reflection surface (53) and a fourth light reflection surface (54) are formed between the first light reflection surface (51) and the second light reflection surface (52) such that these light reflection surfaces (53), (54) make 90 degrees therebetween. According to this optical switch, by changing a region which reflects the light between the upper half and the lower half of the mirror block (50), the coupling relationship between an input optical fiber and an output optical fiber can be changed over.