Provided is a key sheet or a lightproof light guiding sheet guiding light efficiently through an interior of the key sheet and preventing light leakage through a periphery of key tops. On a base sheet, a transparent resin layer, and further, a lightproof dark print layer are provided as needed, with at least one of the transparent resin layer and the lightproof dark print layer being formed of a non-corrosive coating liquid. Further, a smooth surface is formed between the base sheet and the dark print layer.