An input device is provided. The input device includes a key input unit having a plurality of input keys and an input operation unit. A key input monitor monitors a key input to the key input unit. A timer measures a setting time upon the key input. A relay driver is operative to acquire and output an operation signal output from the input operation unit as a control signal and monitor the operation signal. The key input monitor is operative to initiate the timer when the key input to the key input unit is detected and set the relay driver to an output inhibition state. The relay driver is operative to release the output inhibition state such that the control signal is normally output when it is detected that the operation signal is a predetermined operation input within the setting time.