PURPOSE: To facilitate and quicken the adjustment and to avoid the effect of vibration by injecting alumina fine powder to a part of a copper foil pattern of a capacitor formed on a printed circuit board so as to remove the part thereby adjusting the static capacitance.

CONSTITUTION: An automatic trimming device 9 is set to the end of a comb-line parallel plate capacitor 11, the alumina fine powder 10 is injected by compressed air to shape the copper foil, and in moving little by little the injected position, one of the comb-line patterns of the capacitor 11 is separated electrically. Since the capacitor 11 forms a capacitance with the pattern at the rear face of the printed circuit board, the capacitance is reduced by it when one is cut off. Through the adjustment above, the oscillation frequency and the filter characteristic of the oscillator and the filter or the like are easily and quickly adjusted and they withstand the vibration, then the performance is improved.