Patent ID: 8767200

Claim:
A luminous flux branching element, comprising a transparent base member, arranged diagonally to an optical axis, having a plane of incidence and a plane of emission parallel to each other, wherein incident light from the plane of incidence is split into a main luminous flux emitted from an emission position on the plane of emission and a branched luminous flux emitted from a branch position apart from the emission position of which has quantity smaller than that of the main luminous flux, further comprising: a reflecting member arranged on the plane of incidence to cause the plane of incidence to reflect reflected light from the plane of emission, wherein a non-coat region in which antireflection-treated is not performed is formed in a region of the plane of emission where the incident light from the plane of incidence is reached, and antireflection-treated is performed in the plane of emission excluding the non-coat region and the plane of incidence.