two side boards provided apart from each other, each having front part with a top edge and rear part with an upper region;

a keyboard including a plurality of playing keys, provided between said two side boards at the front parts thereof;

a rear top board provided bridging the upper regions of the rear parts of said two side boards, said rear top board having an upper surface;

a fallboard having a substantially flat plate part carrying an outer surface, and an inner surface, a front edge region and a rear edge region, said fallboard pivotably supported to turn about a pivot axis at said rear edge region between said two side boards, and covering said keyboard when said fallboard is closed by turning frontward with said outer surface being horizontal and facing upward, while exposing said keyboard when said fallboard is opened by turning rearward with said inner surface being horizontal and facing upward; and

an accommodation space provided in the form of a recess having a flat-bed part that is substantially flat between said keyboard and said rear top board between said two side boards, and adapted for receiving said fallboard when said fallboard is turned rearward with said inner surface being horizontal and facing upward,

wherein said flat-bed part has a height that keeps said inner surface of the fallboard not higher than said top edges of the front parts of said two side boards when said fallboard is received in said accommodation space, said front edge region including a front skirt for covering front side of said keyboard when said fallboard is closed, said front skirt having a tip edge that positions at a substantially same height as said upper surface of said rear top board when said fallboard is opened,

wherein said top edge of said side board at said front part which is adjacent to said substantially flat plate part of said fallboard is of a substantially same height as said substantially flat plate part in its opened position.