A jig mounting apparatus has a detection optical system that detects reference marker of an eyeglass lens, is configured so as to determine an mounting point based on the reference marker detected by the detection optical system and position the mounting center of jig, which is used in processing the eyeglass lens, on the mounting point to mount the jig on the surface of the eyeglass lens, in which the detection optical system includes: a focusing optical system that focuses a light-emitting optical flux from a light source on the surface of the eyeglass lens, where hidden marks are formed, via an aperture stop; a reflection plate that reflects an optical flux focused by the focusing optical system and passed through the eyeglass lens; and an imaging device that is provided on a position optically approximately conjugate with the aperture stop and configured to focus on a space portion along an optical axis direction from the surface of the eyeglass lens.