A keyboard apparatus for an electronic musical instrument, in which hammers each have increased rigidity without being excessively increased in the mass thereof. The hammers are provided to respectively correspond to keys, and each comprised of a resin hammer base and a metal pipe member which has a circular outer cross-sectional shape and has a fixed end thereof formed at its tip with a flat modified cross-sectional portion which closes an opening at the tip of the fixed end. When the hammer base is injection molded, the fixed end of the pipe member is fixed to a pipe-fixing portion of the hammer base by means of outsert molding. The modified cross-sectional portion of the fixed end achieves a whirl-stop function relative to the pipe-fixing portion.