PURPOSE: To improve the light resistance in a convex axicon for a CO2 laser by grinding a face to be worked to a conical surface parallel to a convex axicon remaining a vertex and its vicinity intact, and grinding the face by a single crystal diamond bit with super precision accuracy.

CONSTITUTION: As before, the flat surface side of a polycrystal of ZnSe, or GaAs is ground, and a face expected to be a conical surface is spherically ground estimating that the spherical surface passes through a cone-vertex and the outer peripheral part. Next, remaining, for example, a spherical surface part of D=100W200μm intact in the center, or the vertex of the cone, the face is ground to a conical surface parallel to the conical surface of a convex axicon to be manufactured. Then the conical surface is ground so as to be an optical surface by a diamond bit with super precision accuracy so that for example, 50μm or less spherical area is remained intact in the vertex of the axicon. Thus, the fracture area is not produced in the cone-vertex, the light refracts and reflects, and the area is not excessively heated, and thus the light resistance can be increased.