The present invention is directed to a streaming system for encrypting encrypted data such as music and image, etc. to perform stream distribution thereof. Client terminals (30) used in this system structure leaves of the hierarchical tree structure, and hold a key set consisting of a route key, node keys and the own leaf key on a path of this tree structure, whereby SDP file is transmitted from a stream server (20). In the SDP file, there is stored encrypted information consisting of EKB including data encrypted by selection key that only specific client terminal holds and encrypted contents key data in which contents key has been encrypted. Only specific client terminal having selection key in key set (selected client terminal) decodes contents key from selection key to decode encrypted contents data caused to undergo stream distribution into contents data to perform real time reproduction thereof.