PURPOSE: To select the lens installed in the lend cylinder having an arbitrary degree number by providing a stepped part on the inside of the front part of the left and the right lens cylinders made of a synthetic resin and fitting and fixing liquid-tightly an arbitrary degree lens to the stepped part through an adhesive.

CONSTITUTION: A stepped part 2 is provided on the inside of the front part of the left and the right lens cylinders 1 made of a synthetic resin. In opposed positions of the lens cylinders 1, a supporting piece 3 is provided, and in a slit 4 provided on the supporting piece 3, both ends of a connector 5 made of rubber are inserted through, and also, subjected to fall-out stop by a detaining part 6. In the periphery of the lens cylinder 1, an overhang edge part 7 is provided so as to run along the face. In the rear end of the overhang edge part 7, a slot 8 in the vertical direction is provided. To the rear face of the overhang edge part 7, a seal material 10 made of independent foam sponge having a window hole 9 is stuck. A degree lens 15 is fitted and fixed liquid-tightly to the stepped part 2 through an adhesive 16, and also, a bent edge of the front end of the lens cylinder 2 is bent and brought into contact on the peripheral edge of the degree lens 15 in a heated and softened state, and a bent edge 17 is formed.