Abstract: A signal processing method for determining base sequence of nucleic acids by subjecting digital signals to signal processing, said digital signals corresponding to an autoradiograph of plural resolved rows which are formed by resolving a mixture of base-specific DNA fragments or base-specific RNA fragments labeled with a radioactive element in one-dimensional direction on a support medium,which comprises steps of:(1) preparing one-dimensional waveform composed of position along the resolving direction and signal level for each resolved row;(2) dividing the one-dimensional waveform into at least two intervals; and(3) smoothing the one-dimensional waveform in every interval through a smoothing means having different characteristics.