PURPOSE: To exactly control the frequency of a main oscillating part, and to obtain an oscillator to oscillate at a stable frequency against a temperature change by using again the output of the main oscillating part as a standard for a temperature detecting part.

CONSTITUTION: The output of the temperature detecting part 3 is counted by a counting part 4 based on the output from the main oscillating part 1. The said output is inputted to a control part 5, and the control part 5 controls a frequency regulating part 2 according to previously set contents in a storage part 6 based on the said input, and regulates the oscillation frequency of the main oscillating part 1. The regulated frequency output of the main oscillating part 1 comes again to be the standard of the counting part 4 to count the output frequency of the temperature detecting part 3. Thus, the exact frequency control of the main oscillating part 1 can be realized, and a oscillator, stable against the temperature change, can be constituted.