A data transforming method is provided which can perform a transforming process of transforming collective order data for a plurality of products into individual order data for each individual product and a transforming process in which order data is inherited to a response data transforming process. For each combination of transform source and destination protocols, various designation information is stored beforehand in a mapping definition information area and transaction data is transferred in accordance with the designation information. Designation information includes information of a request for an individual order data division process and a collective response data collection process and information of a correspondence between data items of transaction data.