PURPOSE: To reduce a current consumption by controlling a booster for boosting an input voltage on a single semiconductor substrate and a frequency divider of an oscillation frequency according to an output of a power source voltage detector provided on the same substrate.

CONSTITUTION: An oscillator 100 oscillates a basic frequency, has a plurality of frequency dividers, and outputs a plurality of clock signals having different frequencies to a booster 102. A power source voltage detector 101 detects a voltage value, and outputs it to the booster 102. The booster 102 has a boosting capacitor 23, and has functions of controlling boosting of an input voltage value and controlling selection of input clock signals. The oscillator 100, the detector 101 and the booster 102 are formed on a single semiconductor substrate. Thus, a current to be consumed is reduced.