An impulse response between a sound-producing source and a listening point in an acoustic space is measured. A frequency characteristic serving as the processing target of sound field correction is derived from the impulse response. A level difference at a boundary frequency between a level representing a low frequency band and a level representing middle and high frequency bands is calculated for the low frequency band equal to or lower than the boundary frequency and the middle and high frequency bands higher than the boundary frequency in the frequency characteristic. The level of a target characteristic in the low frequency band in the frequency characteristic is decided to set the level difference after sound field correction to be equal to or smaller than a predetermined value.