A document retrieval is performed with similarities between documents in numeric data taken into consideration. To this end, generated is a set E of intervals in which each element of a set D of numeric values representing a feature A is included in any one of the intervals. Each numeric value in each document is indexed by assigning, with 1, an interval including an element x of the set D, and with 0, an interval without the element x. Each document data including numeric values is indexed by indexing its text part with term frequencies, and by indexing its numeric-value part with the above-described numeric value indexing scheme. By use of indices thus created for each of the document data, similarities between the document data are calculated using a vector space model or a probability model, and the document data are presented in order of similarity.