1. A method for supporting creation of a classification rule, comprising: storing a new data item and a category of said new data item into a storage; extracting feature patterns each including a condition including a feature element of said new data item stored in said storage and a corresponding category from data stored in a correct answer data storage, which stores data items and categories of said data items, and storing the extracted feature patterns into a feature pattern storage; and grouping said feature patterns stored in said feature pattern storage into a first set whose feature pattern matches with said category of said new data item stored in said storage and a second set whose feature pattern does not match with said category of said new data item, and storing a grouping result into a group data storage.