A neutron measurement apparatus includes: an analog signal processor; a digitizing processor; an FFT calculation processor; and a signal processor. The analog signal processor amplifies alternating current components of detector output signals output from a neutron detector, and filters to remove high frequency components from the output signals, which the digitizing processor digitizes at a constant sampling period in a time series; the FFT calculation processor converts certain of the signals in a time domain from the digitizing processor into signals in a frequency domain, and filters the signals in the frequency domain; and the signal processor selects and extracts signals having required frequency components through the calculation processing on the FFT calculation processor, to calculate power spectral densities of the extracted signals, and to convert the calculated power spectral densities into a neutron measurement value.