PURPOSE: To suppress the variance of the frequency of a trap pole as less as possible and to increase the attenuation degree of trap frequency, by performing the adjustment of the band frequency after deleting or adding a comb-shaped electrode when the production is through with a wafer.

CONSTITUTION: A chip is obtained by vapor-depositing Al on a piezoelectric substrate 1 and then etching a comb-shaped electrode 2 by means of an optional photomask. Then the frequency characteristics are checked by applying a signal input/output terminal to pads of inputs 9 and 10 and outputs 11 and 12 by means of a wafer checker. In this case, the frequency of a trap pole (d) is checked. Then comb-shaped electrodes 5 and 6 are removed by etching with use of a photomask in case the frequency of the pole (d) is drifted inside the band compared with a prescribed frequency. As a result, the frequency of the pole (d) expands toward the outside of the band. Then the trap pole is set at a prescribed frequency. While comb-shaped electrodes 3 and 4 are connected to a pad electrode 9 by a lift-off process and with use of a photomask in the case of a waveform shown by a solid line (b).