PURPOSE: To change over a MOS capacity and to adjust an oscillating frequency by turning on a suitable MOS switch by the selection of the binary code of a selecting terminal incorporated in an IC.

CONSTITUTION: The oscillator is composed of a terminal 1 for oscillation control, a gate terminal 2, a drain terminal 3, a NAND circuit 4, inverters 5 and 6, a buffer 7, an output terminal 8, a built-in capacity 9 which is a reference, a built-in resistance 10, MOS switches 11∼14, inverters 15∼18 for converting a phase, built-in capacities 19∼22 changed over by the MOS switch, selecting terminals 23 and 24, and a decoder circuit 25. When the MOS switch is successively turned one by one with the binary code of the selecting terminals 23 and 24, the MOS capacity can be selected. A capacity value is set more or less higher than the desired oscillating frequency beforehand. When the capacity value of 19∼22 is set so as to come to be larger at the interval of a certain constant value, the whole capacity is changed phasedly and the oscillating frequency is changed. Thus, the frequency can be adjusted.