A cover plate for covering an opening of a casing in which a solid state imaging device is disposed. The cover plate comprises a transparent cover plate member and a conductive film layer. The cover plate hermetically covers the opening of the casing and the conductive film layer covers the outermost surface of the transparent cover plate member. The transparent cover plate member is comprised of a plurality of laminated transparent plates such as lithium niobate plates for an optical low-pass filter and a plate for an infrared cut-off filter. An example of the conductive film layer is a metallic film such as Cr or Au, coated on the surface.