1. A computer program product comprising: a non-transitory computer useable storage 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 total importance of each of electronic documents, based on (i) a plurality of electronic documents chained to each other in a relation of referencing, 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 (a) calculate 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) identify at least one second electronic document which references the given electronic document, on the basis of information referenced; (c) calculate a response coefficient against a first electronic document, on the basis of a degree of similarity between a phrase included in the second electronic document and the response coefficient determining phrase; (d) calculate the total importance of the given electronic document, based on importance unique to one electronic document of the given electronic document, and total importance of the second electronic document; and (e) calculate the total importance of each of the plurality of electronic documents, by applying (a) to (d) to each of a plurality of pairs of the plurality of electronic documents.