An interface for car-mounted devices includes hand data detecting means for determining devices to be controlled among the car-mounted devices based upon hand data corresponding to an operator hand state, voice recognizing means for determining how to change the state of the devices to be controlled based upon an operator voice utterance, and control signal-forming means for forming control signals for the devices to be controlled relying upon the devices to be controlled determined by said hand data detecting means and upon the content of change determined by said voice recognizing means.