A Frequency Modulated Continuous Wave (FMCW) radar using only in-phase channel is advantageous for automotive applications. In this radar, we have to search the pairs of beat frequencies in an up-chirp mode and a down-chirp mode for multiple targets similarly to conventional FMCW radar. However the number of combinations to search pairs is larger than that for the conventional FMCW radar. Therefore, false targets by mistaking the combination of these pairs increase. In this paper, we propose a novel signal processing algorithm to reduce the false targets. We extract only the beat frequencies of the relative moving targets using the differential of the frequency power spectra of the up-chirp mode and the down-chirp mode. We can reduce choosing incorrect pairs by separating stationary targets and moving targets. We have conducted some simulations to confirm the capability of the proposed algorithm. We show that the false target appearance probability is reduced to half or less without significant deterioration of detection probability.