PURPOSE: To reduce the number of the output wiring from a keyboard and to facilitate the judgment of the output of the erroneous digital signal due to the malfunction of a key switch.

CONSTITUTION: This matrix keyboard where plural lines wirings and plural column wirings are arranged by intersecting with each other without contacting, the line wiring and the column wiring are connected at a selected intersecting point B via a diode D, voltage is impressed on the end of each wiring of plural columns via key switches O to F, respectively, a digital. signal in which integer number of '1' corresponding to the depression of each key switch are combined with plural number of '0' is outputted from the output end of each wiring of plural lines, and the line wiring and column wiring are connected at the selected intersecting point B via the diode D so as to output the digital signal in which integer number of '1' which are different from the integer number of '1' are combined with plural number of '0' when more than two of each switch are simultaneously depressed.