1. A character string retrieval method for retrieving at least one of a matching character string and a similar character string, from a retrieval objective character group, to a retrieval character string, the retrieval character string and the retrieval objective character group each having a character code portion and a character pattern portion, comprising the steps of: converting the character code portion in the retrieval character string into a character pattern; pattern matching using the character pattern converted by said converting step and the character pattern portion of the retrieval character string and the retrieval objective character group; code matching using the character code portion of the retrieval character string and the retrieval objective character group; and retrieving the at least one of the matching character string and the similar character string from the retrieval objective character group based on results of said matching steps.