The present invention provides a content transfer system for transferring content from a content transmitting apparatus to a content receiving apparatus through a network in consideration of content protection. The system comprises an authentication process executing means which executes an authentication process between the content transmitting apparatus and the content receiving apparatus to share authentication information therebetween, and a content transfer process executing means which encrypts content to be transferred in response to a content request from the content receiving apparatus to transfer the encrypted content from the content transmitting apparatus to the content receiving apparatus. A transfer process of the encrypted content is started on confirmation that the content request contains a keyword indicating that the content receiving apparatus has been authenticated. The keyword is of a check level that the content transmitting apparatus supports among keywords in a plurality of check levels representing accuracy of authentication check.