There is provided an input device that needs not to change processing of means (a key processor or a key processing microcomputer as a software module) for performing processing based on an on or off state of a key switch in a matrix system and an A/D system. A key-in microcomputer detects the on or off states of plural key switches K based on voltages at A/D input terminals. The key-in microcomputer converts the detected on or off states of the plural key switches K into a bit array. A key processing microcomputer performs the processing based on the bit array converted by the key-in microcomputer.