Alignment marks 12a, 12b, 12c, and 12d are formed on the flat plane 11a of the peripheral edge portion 11 formed integrally with the diffracting layer 8, and when the lens portion 7 is mounted onto the substrate 2, these alignment marks 12a, 12b, 12c and 12d are positioned to the substrate 2, thereby making exact alignment of the diffracting layer 8 with respect to the light detecting portion 4a of the light detecting element 4, for example, not by depending on a difference in curvature radius of the lens portion 7. In particular, the alignment marks 12a, 12b, 12c and 12d are formed on the flat plane 11a, thereby image recognition is given to exactly detect positions of the alignment marks 12a, 12b, 12c and 12d, thus making it possible to make exact alignment.