Key frame has a key support section that pivotably supports thereon a
plurality of keys. Hammer structures are pivotably provided in
corresponding relation to and below the keys, each of which pivots in
interlocked relation to depression operation of a corresponding one of
the keys. On a rear portion of the key frame, there is provided an upper
stopper that is elongated and extends in a direction where the keys are
arranged. The upper stopper defines an upper end limit of pivoting
movement of each of the hammer structures. Opening portion is formed
between the key support section and the upper stopper. Wiring cable
connected to a circuit board, having switches corresponding to the keys,
is run below the key support section, then passed through the opening
portion and thence drawn upwardly beyond the upper stopper so that it is
led out to a region above the upper stopper.