PURPOSE: To compensate effectively fluctuations of a frequency due to a temperature by subtracting a fixed value from the output of an elastic surface wave element with nearly-linear temperature characteristics of delay time and then by supplying an amplifier with the sum of the difference and the output of an elastic surface element whose temperature characteristics of delay time are expressed nearly by the secondary function.

CONSTITUTION: Elastic surface wave element 11 uses crystal for its substrate and temperature characteristics of delay time in terms of the inputting of the output of amplifier 10 are expressed nearly by the secondary function; and elastic surface wave element 12 uses as its substrate material lithium tantalate or lithium niobate and temperature characteristics of delay time in terms of the inputting of the output of amplifier 10 are nearly linear. Here, the output of element 12 is attenuated 14 as much as fixed and the attenuated output is added 16 to the output of element 11 before being supplied to amplifier 10, so that fluctuations of a frequency due to a temperature can effectively be compensated.