A key structure includes a top plate which is formed by laminating a half-transparent resin surface layer member on a resin bottom side member using two-color injection molding, and the top plate is secured on a wooden key base. A plurality of concave grooves and protrusions, and a plurality of protrusion and troughs are respectively formed together in straight lines in the long direction of the key structure on a rear face of the surface layer member and a top face of the rear side member. Outside light is reflected from the top ends of the protrusion and the troughs, whereby a faint and natural vertically-striped pattern, which corresponds to a concave-convex part formed by the concave grooves and the protrusions, is perceived as resembling an edge grain of ivory.