Obtaining a closed pattern in a second itemspace which is made by adding a new item to a first itemspace based on a closed pattern obtained for the first itemspace. To provide a system for detecting a closed pattern, which is a maximum set of items, based on history information which records a set of items that is a target of transaction processing for each transaction. The system records at least a first closed pattern obtained for a first itemspace. The system generates an additional pattern by adding an additional item that is not included in the first itemspace and compares a set of transactions including the whole of the additional pattern with a set of transactions including any of the whole of the first recorded closed pattern. The system detects union of the first closed pattern and the additional pattern as a second closed pattern in the second itemspace, on condition that the compared sets are identical with each other.