PURPOSE: To reduce fluctuation width of an amplitude characteristic more than the width before a correction even if a speaker is changed into a different individual of the same kind by having a constitution that the correction specified amplitude characteristic of a speaker determined by a measurement is averaged with the amplitude values in adjacent frequencies.

CONSTITUTION: The correction characteristic 9 of a speaker 1 is extracted from the difference of a phase linear and flat amplitude characteristic and an amplitude frequency characteristic 8 and the correction characteristic is determined as a frequency base information or time base information. The time information on the correction characteristic 9 of the speaker 1 which is measured by a microphone 7 for characteristic measurement is converted once into frequency base information by using an FFT (high speed Fourier transformation arithmetic unit) 11. Further, as the discrete values obtained on a frequency base, plural adjacent values are selected by a selector 12 and each selected value groups are separately averaged by an averaging arithmetic unit 13. Thus, the averaged value becomes the amplitude value of a new amplitude characteristic 9, this new correction characteristic 9 is converted from the frequency base information to the time base information by an inverse FFT 15 and the characteristic is inputted as the correction characteristic in a non-recursive digital filter 2.