PURPOSE: To compensate fluctuations of a frequency due to a temperature by supplying an amplifier with the output of an elastic surface wave element, having temperature characteristics of delay time similar to the secondary function, phase-shifted by a signal obtained by phase-detecting the output of an elastic surface wave element whose temperature characteristics of delay time are nearly linear.

CONSTITUTION: Elastic surface wave element 11, using crystal for its substrate, has the temperature characteristics of delay time, in terms of the inputting of the output of amplifier 10, expressed nearly by the secondary function and elastic surface wave element 12, employing as its substrate material lithium tantalate or lithium niobate, has the temperature characteristics of delay time, in terms of the inputting of the output of amplifier 10, expressed nearly in a straight line. The output of element 12 is phase-detected 13 by the output of this amplifier 10 and control 17 over how much the output of element 11 is phase-shifted is exercised by the phase detection output before a supply to amplifier 10, so that fluctuations of a frequency due to a temperature can effectively compensated with the simple constitution.