1. A computer-implemented method of detecting, from a first document set and a second document set having a common topic, the document sets having been retrieved on the basis of a term list (a) terms in the second document set that correspond to specific terms in the first document set, and (b) terms in first document set that correspond to specific terms in the second document set, comprising: calculating the probability P(A) of the co-occurrence of a specific term pair, which includes a term from the first document set and a term from the second document set; calculating the probability P(B) of the lack of co-occurrences of the first term of a term pair in question occurring in the first document set and the second term of said term pair not occurring in the second document set; calculating a maximum likelihood ratio on the basis of P(A) and P(B); extracting all term pair combinations having a maximum likelihood ratio that exceeds a predetermined threshold value; selecting, using a processor, a predetermined number of terms in a descending order of values of maximum likelihood ratios from the terms in first document set that correspond to a specific term in the second document set, and adopting the selected terms as the candidate terms of the first document set that correspond to specific terms in the second document set; and selecting, using the processor, a predetermined number of terms in a descending order of maximum likelihood ratios from the terms in the second document set that correspond to a specific term in the first document set, and adopting the selected terms as the candidate terms of the second document set that correspond to the specific terms in the first document set.