A contents supply apparatus supplies sub-content that relates to main content. A DVD-ROM stores a bind key unique to the DVD-ROM and main content that is a digital work. A main player reads the bind key from the DVD-ROM, acquires sub-content that relates to the main content stored on the DVD-ROM, generates encrypted sub-content by encrypting the acquired sub-content based on the read bind key, and writes the generated encrypted content to an SD memory card. A sub-player reads the bind key from the DVD-ROM, reads the encrypted sub-content from the SD memory card, generates sub-content by decrypting the read encrypted sub-content based on the bind key, and plays back the generated sub-content.