A keyboard circuit (15) of an electric music instrument includes contact transistors (TRk) having at least three terminals as input/output terminals for state detection for each of a plurality of contacts (14a, 14b, and 14c); and wiring units to the contact transistors (TRk) and the contacts (14a, 14b, and 14c). A selector (Sm) and the wiring unit for each of the plurality of contacts (14a, 14b, and 14c) are arranged to be divided into a plurality of layers in three dimensions. Then, the keyboard circuit (15) detects ON/OFF states for each of the contacts (14a, 14b, and 14c) for which the ON/OFF states change in response to a key-pressing operation for each of a plurality of keys (12) and for which at least one is provided to each of the plurality of keys (12).