To provide a technique which involves a key sheet integrally including a light guide sheet and having a plurality of illumination areas, the technique preventing light leakage from the boundary between the individual illumination areas and providing high durability against a repeated pressing operation. A mask layers cover the opening edges of slits of a light guide sheet on the operation surface side. The mask layers can prevent emission of light from the openings of the slits to the outside, the light having leaked from the end faces of the light guide sheet, and the end faces forming the slits. A front sheet and a back side cover can enhance the durability of a base sheet, the front sheet adhering to the light guide sheet so as to cover the slits.