In an absorption type multi-layer film ND filter having a thin substrate and provided thereon first and second absorption type multi-layer films which attenuate transmitted light, the first and second absorption type multi-layer films are constituted of multi-layer films each consisting essentially of dielectric layers formed of SiO.sub.2, Al.sub.2O.sub.3 or a mixture of these and metal film layers formed of Ni alone or an Ni alloy; the layers being alternately layered on the substrate; and the first and second absorption type multi-layer films are so formed on one side and the other side, respectively, of the substrate as to have a film structure in which they are symmetrical to each other interposing the substrate between them, and the warpage of the substrate has been controlled at a curvature of radius of 500 mm or more.