Abstract: A keyboard instrument such as an upright piano is basically constructed by a keyboard, an action, a case assembly, a fall assembly, a back hollow assembly and a top door assembly. Herein, the fall assembly provides a fall cover for covering the keyboard, and the top door assembly having an opening top door is linked to the fall assembly by way of the back hollow assembly. The top door pivotally moves in response to movement of the fall cover of the fall assembly being closed or opened, wherein when the fall cover is opened, the top door opens to produce a small gap in proximity to a lower end of the top door. The small gap allows piano sound to be partially released from a casing to increase loudness of the piano sound and to enhance clarity in tone color of the piano sound. The keyboard instrument further provides a damping mechanism for imparting resistance load to the fall cover being closed or opened.