A keyboard musical instrument comprises a keyboard having a plurality of playing keys, a fallboard pivotably supported at its rear end for covering the keyboard when the instrument is not in use and exposing the keyboard when the instrument is in use, and a rear top board. An accommodation space is provided between the keyboard and the rear top board and is adapted for receiving the fallboard which turns through 180 degrees to wide open the space from above the keyboard through above the rear top board. Thus, while the instrument is in use, the fallboard will obstruct neither the player's view nor the sound propagation from the loudspeakers, and further the fallboard will help in supporting the music sheets.