A mounting part for mounting spectacle frame components such as lugs can be machined after confirming that a lens thickness at a mounting part-machined portion where the mounting part is machined is equal to or larger than the specified value, and can be installed the spectacle lens components on the spectacle lens with a requested strength. The device, the method for the above, a spectacle lens manufacturing method, and a spectacles manufacturing method are given. The spectacle lens (1) is fed to a lens thickness measuring device (70) by a lens feeder. The fed amount of the spectacle lens in this feeding is based on the measured results of a distance between a frame center forming a block center by a lens holder in an edging for manufacturing the spectacle lens (1) from a raw material lens and the edge face of the spectacle lens (1) where the mounting part is to be machined. The thickness of the lens at the mounting part-machined portion can be accurately measured by the measuring device (70) even if an error produced in the edging is included in the distance.