However, the conventional image display devices of the aforementioned types have problems such as, for JP 2005-352024 A, an optical unit is embedded in a lens part of a pair of eyeglasses, therefore an existing pair of eyeglasses cannot be used, for JP 3871188 B2, even if an optical unit has a foldable structure, folding work of the optical unit is required separately from the folding work of a te