A radar signal processor is disclosed having an observation mechanism for receiving a reflected wave from a target and for outputting a predetermined observation signal. The processor extracts a distance component corresponding to a distance from each observation signal. The processor further collects the respective distance components and computes an estimated value of a corresponding correlation matrix with a forgetting factor as a parameter using a method for estimating correlation matrix with exponential smoothing. The processor further estimates the presence or movement state of the target on the basis of the respective estimated values of the correlation matrices and outputs the computed values.