PURPOSE: To reduce the power consumption by driving a reference voltage generating circuit for an A/D conversion, only in the case of executing an A/D conversion processing.

CONSTITUTION: To a reference voltage generating circuit 9 for applying a reference voltage for an A/D conversion to an A/D converter 10, a control signal (a) for driving is applied from a CPU 1 through an input/output port 7. For instance, when the control signal (a) is an H level, the reference voltage generating circuit 9 operates and applies a reference voltage to the A/D converter 10, and wen the control signal (a) is an L level, the reference voltage generating circuit 9 is controlled so as to become a stop state. The A/D converter 10 converts an analog input signal to a digital signal, based on a command of the CPU 1. In such a way, the A/D conversion use reference voltage generating circuit 9 is controlled so as to become a driving state only at the time of executing an A/D conversion, therefore, while the A/D conversion is not executed, no power is consumed. Therefore, the power consumption can be reduced.