PURPOSE: To match an oscillating frequency to a desired frequency accurately by matching the oscillation frequency with the desired frequency after a surface acoustic wave oscillator is assembled.

CONSTITUTION: A surface acoustic wave oscillator 6 and peripheral electronic circuits 7a-7c are assembled in one package 4 and in the stage when all components except a cap of the package 4 are mounted, a plate 3 having a proper shaped hole is mounted in place of the cap of the package 4. The surface acoustic wave oscillator in this state is placed in a chamber of a reactive ion etching device to oscillate the surface acoustic wave oscillator and the surface acoustic wave resonator 6 in the package 4 is subjected to reactive ion etching while measuring the oscillating frequency to make fine regulation of the oscillating frequency of the surface acoustic wave oscillator. Thus, the oscillating frequency is accurately fine-regulated without being affected by characteristic dispersion of electronic components or the like.