Musical keyboard instruments have a long history, whichresulted in many kinds of keyboards (claviers) today. Sincethe hardware of conventional musical keyboards cannot bechanged, such as the number of keys, musicians have tocarry these large keyboards for playing music that requiresonly a small diapason. To solve this problem, the goal ofour study is to construct UnitKeyboard, which has only 12keys (7 white keys and 5 black keys) and connectors fordocking with other UnitKeyboards. We can build variouskinds of musical keyboard configurations by connecting oneUnitKeyboard to others, since they have automatic settingsfor multiple keyboard instruments. We discuss the usabilityof the UnitKeyboard from reviews by several amateur andprofessional pianists who used the UnitKeyboard.