To restrain unauthorized use without impairing convenience for a data user, when using a content, and to surely protect a copy right.

This method is provided with a data use history preparing means 3 for preparing data use history information ct including a use start time c1 and a use finish time c2, when using a data b by a data using means 1, a data use history transmission means 5 for transmitting the data use history information ct to an outside, a data use history reception means 6 for receiving data use history information cr from the outside, and a data use history comparison means 7 for comparing the respective pieces of data use history information, and for issuing duplicated device use notification information d for indicating the generation of duplicated data use time, when the data use time obtained based on any of pieces of data use history information included in the data use history information ct is duplicated with the data use time obtained based on any of pieces of data use history information included in the data use history information cr.

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