A signal cutting-out unit cuts out a signal reflected from a target by a specific length while the cut-out signals are overlapped by a set length. A power spectrum calculating unit calculates a plurality of power spectra from output signals from the signal cutting-out unit. A power spectrum reconstructing unit performs power spectrum reconstruction by changing a ratio or contribution rate of power spectrum components in a set region, using the plurality of power spectra. A spectral moment calculating unit calculates a spectral moment from a power spectrum reconstructed by the power spectrum reconstructing unit.