An approximately rectangular parallelopiped shaped optical element 100 has a substrate (base) 101, a lens 102, and an axially symmetric convex portion 103D formed in an upper surface 100U of the substrate 101. The radius of curvature of the surface of this convex portion 103D is approximately constant. The substrate 101 has an axially symmetric concave portion 101B in a bottom surface 100B of the substrate 101. A radius of curvature of the surface of this concave portion 101B is approximately constant. The concave portion 101B is filled with an optical material having a refractive index different from the substrate 101, thereby forming the lens 102. A flat portion 103E is formed around the convex portion 103D. Axes of symmetry of the convex portion 103D and the concave portion 101B are positioned on an identical straight line and are vertical with respect to the flat portions 103E and 101C.