KEYBOARD CIRCUIT, AND DETECTING METHOD FOR THE SAME

PROBLEM TO BE SOLVED: To enable the number of wires for a substrate for keyboard switches to be so significantly reduced that only one face of the substrate would be sufficient for the wiring.SOLUTION: A keyboard circuit 15 of an electronic instrument is provided with a contact-connecting transistor having three or more terminals each as an input/output terminal for state detection of one or another of multiple contacts 14a, 14b and 14c, and a wiring part for connection to the contact-connecting transistor and the contacts 14a, 14b and 14c, and selectors, one for each of the multiple contacts 14a, 14b and 14c and the wiring part, are arranged as three-dimensionally divided into a plurality of layers. The keyboard circuit 15 detects the on/off state of each of the contacts 14a, 14b and 14c, of which one or more are provided for each of multiple keys 12, whose on/off state varies in response to pressing of each of the multiple keys 12.