The scale conversion unit 215 performs scale conversion from the envelope data to data that are logarithmically equally spaced (S2). The scale conversion unit 215 interpolates data in a low frequency band in which data points are sparcely spaced, using three-dimensional spline interpolation or the like. This processing causes scale converted data in which data points are equally spaced on the logarithmic frequency axis to be obtained. The scale conversion unit 215 may perform scale conversion, using, without being limited to the logarithmic scale, various types of scales described afore.

The normalization factor computation unit 216 computes a normalization factor, using weights for each frequency band (S3). To the normalization factor computation unit 216, weights are set with respect to each of a plurality of frequency bands in advance. The normalization factor computation unit 216 extracts characteristic values of the scale converted data with respect to each frequency band. The normalization factor computation unit 216 computes a normalization factor by performing weighted addition of the plurality of characteristic values.

The normalization unit 217 computes a normalized ECTF, using the normalization factor (S4). The normalization unit 217 computes a normalized ECTF by multiplying the ECTF in the time domain by the normalization factor.

The transform unit 218 computes a frequency response of the normalized ECTF (S5). The transform unit 218 computes a normalized power spectrum and a normalized phase spectrum by performing discrete Fourier transform or the like on the normalized ECTF.