To offload a microcontroller from many functions and to turn the microcontroller into an inoperable state as much as possible for saving the power by a control circuit.

Function signals are supplied to this control circuit 2 and the function signals are related to the functions set beforehand of a radio part 12, a cassette deck 13 and a CD exchanger 14 controlled by a microcomputer 1. The control circuit 2 supplies read request signals to the microcontroller 1 when the function signals change. By the read signals, the microcontroller 1 evaluates changed external signals and/or reads data relating to the signals. When the microcontroller 1 is in the inoperative state when the function signals change, the control circuit 2 supplies reset signals to the microcontroller 1 before supplying the read request signals.