PURPOSE: To save the developing time and cost of a keyboard input device by using a key matrix attaining various key arrays without using an exclusive key controller or an I/O handler.

CONSTITUTION: A key controller 4 successively outputs scanning signals to input lines T5 to TE. Each scanning signal is transmitted to one or two scanning signal lines in accordance with the set status of a row connecting circuit 2. If a key contact corresponding to a line to which the scanning signal is outputted is closed at the time of its output, a return signal is generated. The return signal is transmitted to an output line determined in accordance with the set status of a line connecting circuit 3 and appled to the controller 4. At the time of detecting the return signal, the controller 4 identifies the closed key contact. Since the key matrix 1 is used, various key arrays can be attained.