3. The synonymous term generating method as claimed in claim 1, which further comprises the step 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 other words which are unrelated to the target character string based on a predetermined rule.
3. The synonymous term generating method as claimed in claim 1, which further comprises the step 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 other words which are unrelated to the target character string based on a predetermined rule. 4. The synonymous term generating method as claimed in claim 3, wherein said predetermined rule is prescribed by a distance so that a number of words forming the target character string is n, the distance between two mutually adjacent words is "1", a value n which is identical to the number of words forming the target character string is set as a maximum distance, and the synonymous terms of the target character string are generated at a distance less than or equal to said maximum distance.