An efficient analysis method in the frequency domain for the extraction of information under the degradation of signal-to-noise ratio is proposed. When the electromagnetic emission from the cryptographic module on the hardware is analyzed, the electromagnetic fields caused by operations on the other modules interfere to the electromagnetic field from the cryptographic module. Therefore, the amount of the measurement data required for the extraction of information under the condition of degraded SNR increases and the analysis for this increase of data needs additional computation time. In order to accelerate the analysis under the degradation of SNR, we focus on only the processing for analysis target data. Furthermore, the signal of information and noises is separated with the analysis on the frequency domain. The proposed method is examined through experiments.