In an optical element (B1) prepared by integrally forming, on surfaces of a transparent member, a refracting surface (R2) for receiving a light beam, a plurality of reflecting surfaces (R3, R4, R5) with curvatures, and a refracting surface (R6) for outputting the light beam reflected by the plurality of reflecting surfaces, a reference portion (7) for defining the position of the optical element in a predetermined direction with respect to a Y′-Z′ plane including an incident reference axis (5) and an exit reference axis (5) of at least one reflecting surface of the optical element (B1) is formed on the optical element.