A technique for sharing contents data in a network. In order to easily share the contents data in the network without using a physical media apparatus or a personal computer, a contents data providing device for providing the contents data is registered in a server in the network, and after the registration, the contents data is transmitted to the server. A contents data receiving device for receiving the contents data is registered in the server, and after the registration, the registered contents data receiving device is authenticated. According to a result of the authentication, the contents data is transmitted to the contents data receiving device.