PURPOSE: To realize a temperature compensated crystal oscillator whose size is made small with comparatively small power consumption.

CONSTITUTION: The oscillator is provided with a thermosensing element 5 sensing ambient temperature to provide temperature information, an A/D converter 8 converting the temperature information provided by the thermosensing element 5 into a digital signal, a nonvolatile memory 6 providing the output of temperature compensation data stored in advance corresponding to the temperature information converted into the digital signal by the A/D converter 8, a D/A converter 9 converting a digital signal outputted from the nonvolatile memory 6 into an analog voltage, and an oscillation circuit 4 whose oscillated frequency is adjusted based on the temperature compensation data converted into an analog voltage by the D/A converter 9 and all the components above are integrated-circuited on a common substrate.