This storage system is designed to: divide data into a plurality of chunk data (pieces of data) in a deduplication process; select one or more chunk data from among the plurality of chunk data in accordance with a sampling period which indicates that, on average, one chunk data be selected from among each N chunk data; and calculate a fingerprint, such as a hash value, for each of one or more characteristic chunk data, which are the selected one or more chunk data, and determine whether data including the one or more characteristic chunk data is a duplication. The storage system changes the sampling period on the basis of the results of past deduplication processes.