1. A computer program product comprising a computer useable medium including a computer readable program, wherein the computer readable program when executed on a computer causes the computer to function as a system for calculating the total importance of each of electronic documents, based on (i) a plurality of electronic documents chained to each other in a relation of referencing and being referenced, from a start electronic document which is not referenced by any other electronic document to a terminal electronic document which does not reference any other document, (ii) information on relation of referencing and being referenced, (iii) an important phrase, and (iv) a response coefficient determining phrase, (i) through (iv) being stored in a storage device, the computer program causing a computer to operate as: (a) means for calculating the importance of a given electronic document among the plurality of electronic documents, on the basis of the degree of similarity between the important phrase and a phrase included in the given electronic document; (b) means for identifying at least one second electronic document which references the given electronic document, on the basis of the information on relation of referencing and being referenced; (c) means for calculating a response coefficient against the first electronic document, on the basis of the degree of similarity between a phrase included in the second electronic document and the response coefficient determining phrase; (d) means for calculating the total importance of the given electronic document, based on the own importance of the given electronic document, and the total importance of the second electronic document; and (e) for calculating the total importance of each of the plurality of electronic documents, the means applying the means (a) to (d) to each pair of the plurality of electronic documents.