To provide an optical device assembling method which for stacking and connecting the lens holders (lens cells) holding ultraviolet lenses which are the optical elements to each other without stressing the optical elements by connecting them at their outside surfaces, and provide a tool for connecting them and a method of connecting or separating them by using this tool.

This optical device assembling method prepares lens holders 2 having projecting rings 7, 8 for holding optical elements (ultraviolet lenses L) and extending around their both ends, and connectors 11 having a first and a second claws (12b, 14) movable to approach each other, then stacks those lens holders 2 overlapping their ends one another. It connects the adjoining lens holders 2, 2 with the connectors by pinching their projecting rings 7, 8 with the first and second claws (12b, 14) of the connectors 11.