An optical thin film formed by laminating, from the substrate side, an interlayer, a silver-containing metal layer that contains silver, and a dielectric layer, in which an anchor metal diffusion control layer provided between the interlayer and the silver-containing metal layer, an anchor region which includes an oxide of the anchor metal and has a surface energy that is less than the surface energy of the silver-containing metal layer and larger than the surface energy of the anchor metal diffusion control layer is provided between the anchor metal diffusion control layer and the silver-containing metal layer, a cap region which includes an oxide of the anchor metal is provided between the silver-containing metal layer and the dielectric layer, and the total film thickness of the silver-containing metal layer, the anchor region, and the cap region is 6 nm or less.