The invention relates to a radar device and a signal processing method for the radar device. The radar device is provided with an object targeting unit (S150) that radiates radar waves and recognizes a detection subject using reflected waves. The object targeting unit extracts, as a target, a peak that is among peaks extracted from a power spectrum generated by means of frequency analysis and that is recognized to have a historical connection across a measurement cycle that is at least a pre-set object targeting threshold. A rain determination unit (S410, S420) determines that there is rain when the misdetection count, which is the number of peaks detected until the previous measurement cycle by means of the object targeting unit that were not confirmed to have a history connection with a peak detected in the current measurement cycle, is greater than a pre-set rain determination threshold. A parameter updating unit (S430) updates the object targeting threshold in a manner so as to be higher the greater the misdetection count when the rain determination unit has determined that there is rain.