A beam splitter is constructed from three light transmissive members formed of a glass or plastic that are bonded together to form a rectangular parallelepiped when taken as a whole. First and second light separating surfaces are formed at the bonding surfaces of the first and second light transmissive members and the bonding surfaces of the second and third light transmissive members, respectively. Accordingly, three light beams can easily be formed from a single beam of incident light.