A storage-medium rental system includes a portable storage medium to be rented to the user, a portable semiconductor memory owned by the user, a rental-shop apparatus owned by the rental agent, and a reproduction apparatus owned by the user. The storage medium prestores encrypted content which is generated by encrypting digital work by using a content encryption key. The semiconductor memory has an area for securely storing a content decryption key. The rental-shop apparatus stores a content decryption key for decrypting the encrypted content. The rental-shop apparatus writes the content decryption key to the semiconductor memory. The reproduction apparatus securely reads the content decryption key from the semiconductor memory, reads the encrypted content from the storage medium, decrypts the encrypted content by using the content decryption key, and reproduces the decrypted content.