PURPOSE: To realize the small sized inexpensive oscillator with high accuracy and high performance by using a data control circuit so as to control a capacitor array with an external data at the check process and with a data of a nonvolatile storage circuit in use.

CONSTITUTION: An optimum data structure closest to set a frequency on request to the oscillator is decided by monitoring the frequencies with some sets of data combinations at the check and the decided data is programmed to a PROM 106 by the control of a write circuit 109. A data selection circuit 509 activates clocked inverters 505-508 in the usual operating state of the oscillator and a switched capacitor array 103 is controlled by a data in the PROM 106. In the actual use, the three modes such as the frequency adjustment, the program and the normal use mode are provided, and the manufacturer uses the frequency adjustment mode and the program mode for checking in the check process, and the oscillator adjusted and shipped oscillates a frequency with high accuracy. The user uses the usual operating mode.