This invention is to appropriately support creation of a classification rule for a new data item. This method includes: storing a new data item and a category of the new data item into a storage; extracting feature patterns each including a condition including a feature element of the new data item stored in the storage and a corresponding category from data stored in a correct answer data storage, which stores data items and categories of the data items, and storing the feature patterns into a feature pattern storage; and grouping the feature patterns stored in the feature pattern storage into a first set whose feature pattern matches with the category of the new data item stored in the storage and a second set whose feature pattern does not match with the category of the new data item, and storing a grouping result into a group data storage. Accordingly, the feature pattern, which is a candidate of the classification rule, is automatically generated, and furthermore, it becomes possible to select a specific feature pattern as a classification rule to be applied hereinafter from the first set.