According to the present invention, there is disclosed a control circuit in which a D/A converter having an output voltage switchable based on a set value held in a register, an operation amplifier including two input terminals and one output terminal, and a switch for selectively inputting an output of the D/A converter into one of two input terminals of the operation amplifier are constituted on the same chip. The input terminal which has not been selected by the switch and the output terminal of the operation amplifier are connectable to an external circuit.