A key delivery apparatus that prevents improper use of contents, and manages a decryption key for decrypting encrypted content and a suppliable number showing how many times the decryption key is suppliable, with respect to one or more terminal apparatuses connected to a network. The key delivery apparatus receives a supply request for the decryption key from a terminal apparatus, and if the terminal apparatus is a legitimate supply target, judges whether the terminal apparatus is a first-type that manages a content-usage period or a second-type that does not manage the content-usage period, and if the suppliable number has a remaining number, supplies to the terminal apparatus, the decryption key and a key-usage period of the decryption key when judged that the terminal apparatus is the first-type and the decryption key when judged that the terminal apparatus is the second-type.