An instrument main body has a keyboard including a plurality of keys and sound generators (for example, speakers) at a rear of the keyboard. At the rear of the keyboard, an upper surface cover portion composed of an upper panel, a operating panel, and so on is provided to cover an upper portion of the instrument main body. In the operating panel, tone escape portions are provided at right and left regions separated in a direction in which the keys of the instrument main body are arranged. Further, a rear panel is erected on the upper panel at a rear of the tone escape portions and having a width equal to or larger than the entire width of the keyboard in the direction in which the keys are arranged and a height larger than the length of the key in its longitudinal direction.