Data duplication detection system and method for controlling data duplication detection system

Accurate and efficient detection of data duplication is implemented. A data duplication determination part (1A) of a storage system (1) temporarily stores in a pool (4) a target chunk data when a second management table (T2) indicates that the target chunk data, which is included in received data, has already been stored, and, in addition, when data (a fingerprint (FP)) for guaranteeing the identity of the target chunk data is not stored in a third management table (T3). The duplication determination part (1A), in a case where the second management table indicates that another target chunk data that differs from the target chunk is already stored, and, in addition, in a case where determination is made that the FP of the other target chunk data is stored in the third management table, makes a redetermination as to whether the chunk data stored in the pool has already been stored.