To fix a rim guide and a lens more tightly and prevent the lens from falling by providing one ring-shaped structure having no break so that part of a band fits the joint part between the lens and a rim and also fits the entire circumference of the lens end surface.

A 1st band is composed of a 1st joint part and a 2nd joint part which are fit-inserted in a recessed part formed in the rim guide. The 1st joint part of the 1st band is fit-inserted in the recessed part 4 first. Then the 2nd joint part protrudes. This 2nd joint part which protrudes is depressed into the recessed part 4 formed at the upper part of the lens 1. Then the 1st fixation of the rim guide 2 and lens 1 is attained. Then a 2nd band 2 is joined with the end surface 10 of the 1st band which is already fitted in. Then the both form the complete ring-shaped structure. The lens 1 is clamped between the 2nd band and rim guide 4 by utilizing the tension of the 2nd band.