A delivery of content to the unspecified number of persons is prevented by limiting the content delivery range. A delivery source terminal 110 generates an authentication code based on the number of possible transmission times of content and an authentication code key 116, and configures the number of possible transmission times and the generated authentication code in a packet. The delivery source terminal 110 transmits the packet to a delivery destination terminal 130. A router 120 verifies whether the authentication code generated based on the number of possible transmission times and the authentication code key 124 that are received agrees with the authentication code received from the delivery source terminal 110, updates the number of possible transmission times when the two codes agree, generates a new authentication code, and configures it in the packet. The router 120 transmits the packet thus generated to the delivery destination terminal 130.