To perform control to automatically change a key range dividing position according to a performance state of a player.

With this key range dividing device, a keyboard 15k consisting of a plurality of keys C1 to C6 is divided into a plurality of key ranges Kα, Kβ by key range dividing positions S=Sa to Sc, and individual musical sound control characteristics α, β are allocated to the respective key ranges Kα, Kβ, and the positions of the player's hands AL, AR;...;L, R on the keyboard 14k are detected by a hand detection part. Then, the key range dividing position S is dynamically controlled according to the hand positions detected with the keyboard performance of the player, for example, the key range dividing position S is automatically set between the two hands AR, BL in the central part of the keyboard or between the right and left hands (a2, b2). Moreover, if the right and left hands are crossed to come into a different positional relation from a normal one, the new key ranges Kα, Kβ are set to the reversed musical sound control characteristics β, α. In the case of two-person performance, it is possible to set the key range dividing position S with the position of a specific kind of hand (for example, AR) of a specific player prioritized.