A musical instrument is provided. When the lid is revolved in a direction to open the lid from a close state of the lid, the guided part is guided to an inner peripheral concave surface of the guiding channel and is engaged with the inner peripheral concave surface. The lid is supported by the bearing bar 30, and the lid is maintained being up. After the lid is revolved in a direction to further open the lid from the open state and the guided part is disengaged from the inner peripheral concave surface, the lid can be laid down by revolving in a direction for laying down the lid. Therefore, the lid can be changed to an open state or a close state by only revolving the lid.