A musical instrument comprises a keyboard assembly including juxtaposed keys and juxtaposed swing weight mechanisms, each of the keys correspondingly linked with each of the swing weight mechanisms. The keyboard assembly is supported on a key bed having an aperture which is elongate in the direction of the key juxtaposition. Actuating members are provided corresponding to the respective swing weight mechanisms each of which in turn actuates each corresponding key. The actuating members are disposed in a lower yoke having a channel member and flanges integrally manufactured by bending a metal plate. The flanges are fastened to the key bed across and over the aperture so that the actuating members penetrate the aperture toward the swing weight mechanism. The height of the channel member determines a relative position between the actuating members and the swing weight mechanism.