1. A method for supporting creation of a classification rule, comprising: first extracting, by a processor of a computer that accesses a correct answer data storage unit storing correct answers each including a data item and a corresponding first correct category of the data item, and a classification rule storage unit storing classification rules each including a condition part that includes at least one keyword and a corresponding second category, a plurality of feature patterns from the correct answer data storage unit, wherein each of the plurality of feature patterns includes at least one feature element included in a new data item inputted by a user and a first correct category corresponding to a data item including the at least one feature element; second extracting, by the processor, one or plural classification rules whose condition part satisfies the new data item from the classification rule storage unit; grouping, by the processor, the plurality of feature patterns into a first group of feature patterns that are satisfied with a condition part of one classification rule included in the one or plural classification rules extracted in the second extracting and have a first correct category different from a second category of the one classification rule, a second group of feature patterns that are satisfied with the condition part of the one classification rule and have a first correct category identical to the second category of the one classification rule, and a third group of feature patterns that are not satisfied with the condition part of each of the one or plural classification rules extracted in the second extracting; and outputting, by the processor, data of the first group in association with the one classification rule, data of the second group in association with the one classification rule and data of the third group in association with data representing that no condition parts of the one or plural classification rules satisfy feature patterns included in the third group.