A content import method in a digital rights management (DRM) system imports transport streams received from outside a domain, generates a content file, and regularly inserts information in the form of transport packets necessary for decrypting encrypted content into a payload of the content file. Accordingly, even if usage constraint information (UCI) included in the received content changes, packaging is possible. When a device pertaining to the domain receives half of an imported content file via streaming, transport packets of the received half of the imported content file can be promptly decrypted without a time delay.