The rim frame and the lens are continuously restrained to each other over a range other than the gap to stabilize holding of the lens while attachment and detachment of the lens can be facilitated by expanding a gap as consolidating the gaps in the two places into one place due to the deflection of the rim frame and movement of the lens in the left-right direction, whereby the lens can be easily attached and detached without using a tool such as a screwdriver, while can achieve holding stability when fixing the lens and ease of attachment and detachment.