8. The synonymous term generating method as claimed in claim 1, which further comprises the steps of: (d) generating the synonymous terms of the target character string by using at least two selected words or synonymous terms obtained by said step (b); and (e) generating the synonymous terms of the target character string by using at least two selected words or synonymous terms obtained by said step (b) and other words which are unrelated to the target character string based on a predetermined rule.
8. The synonymous term generating method as claimed in claim 1, which further comprises the steps of: (d) generating the synonymous terms of the target character string by using at least two selected words or synonymous terms obtained by said step (b); and (e) generating the synonymous terms of the target character string by using at least two selected words or synonymous terms obtained by said step (b) and other words which are unrelated to the target character string based on a predetermined rule. 10. The synonymous term generating method as claimed in claim 8, wherein the synonymous term file which is used for the retrieval in said step (a) also defines different sounding synonyms of the words as the synonymous terms of the words and defines the relationship of the words and the synonymous terms in a hierarchial relationship, said different sounding synonyms being synonyms which sound differently.