This paper proposes a way to implement a time-domain blind separation algorithm for convolutive mixtures of source signals. The approach provides another form of the algorithm by discrete Fourier transform and has the possibility of designing a separating filter in the frequency domain, without bothering about the permutation problem inherent in frequency-domain blind separation approach. This paper also shows a technique to improve separation performance in the frequency domain. The validity of our approach was demonstrated by performing an experiment on separation for convolutive mixtures of two speeches.