An observation signal processing apparatus transmits pulse signals as search signals per each search, generates observation values based on reflected signals against a target and delay modulation pulse signals, and performs coherent integration on the observation values to output an integration value. The apparatus includes a section for storing a coherent integration count, a section for transmitting pulse signals equivalent to the coherent integration count, a section for calculating a phase correction amount based on an estimated relative speed, and a section for performing phase-weighted coherent integration on the observation values based on the phase correction amount.