A radar signal processing unit comprises a Fourier transform section 1 for executing Fourier transform of the received signal to a frequency signal, a frequency domain power calculation section 2 for calculating a power spectrum of electric power for each frequency from the frequency signal, an abnormal echo removal section 3 for determining the abnormal echo based on the power value of the power spectrum and outputting only the power spectrum not corresponding to the abnormal echo, an incoherent processing section 4 for performing incoherent integration of only the power spectrum not corresponding to the abnormal echo and averaging, and a signal detection section 5 for calculating the physical quantity of the atmosphere from the incoherent-integrated power spectrum.