PURPOSE: To simplify a connection part where an output signal is led out without being affected by the number of keys by arranging sheet resistances in array along a key array, passing voltage applied to one end of a sheet resistance by the depression of a specific key through the key and dividing it by the resistance, and converting the divided voltage into a digital voltage and detecting the key input position.

CONSTITUTION: The power source connection part 6 and ground connection part 7 at the tip parts of a sheet resistance layer 5 are connected to a power source and the ground and the voltage applied between the power source connection part 6 and ground connection part 7 is equally divided by the sheet resistance layer 5. Further, a sheet 4 is provided with another sheet 8 below it while keeping a gap with spacers, and a conductive layer 9 provided to the sheet 8 is connected to the input terminal of an A/D converting circuit. And, the A/D converting circuit reads the input voltage and discriminates the key input corresponding to the voltage data. Consequently, the part where the output signal is led out can be simplified without being affected by the number of keys, and a time difference in key read can be eliminated.