a plurality of keys;

a key frame that pivotably supports said plurality of keys by a key support section thereof;

a circuit board provided below the keys and having switches corresponding to the keys;

a plurality of hammer structures pivotably provided on said key frame in corresponding relation to and below the keys, each of said hammer structures pivoting in interlocked relation to depression operation of a corresponding one of the keys;

an upper stopper provided on a rear portion of said key frame and elongated and extending in a direction where the keys are arranged, said upper stopper defining an upper end limit of pivoting movement of each of said hammer structures, an opening portion being formed between the key support section and said upper stopper; and

an upwardly-opening wall section provided on said key frame above said upper stopper in positional correspondence with said opening portion formed between the key support section and said upper stopper,

wherein a wiring cable connected to said circuit board is run below the key support section of said key frame, then passed through the opening portion and thence drawn upwardly beyond said upper stopper so that the wiring cable is led out to a region behind said key frames,

wherein the wiring cable drawn upwardly beyond said upper stopper through the opening portion is led out rearwardly to the region through an upward opening of the wall section, and

wherein the upward opening of the wall section is located at a same height as or higher than an uppermost end of said hammer structures when said hammer structure are held by said upper stopper.