A signal processing device, includes: an azimuth estimation unit configured to estimate an arrival azimuth of a radio wave based on a reception signal of plural antennas; an estimated reception signal calculation unit configured to calculate an estimated reception signal based on an estimation result of the arrival azimuth, for comparison with the reception signal; a residual signal calculation unit configured to calculate a residual signal which is a difference between the reception signal and the estimated reception signal; and a determination unit configured to determine whether the estimation result of the arrival azimuth is correct based on the residual signal.