To provide an image data recorder and its method, and an image data reproducing device and its method by which illegal use of image data can be prevented.

A memory card 30 stores a media ID that is specific to the memory card 30 and a device ID memory 11 of a camera stores a device ID that is specific to the camera. When image and audio data are obtained, 1st encryption is applied to the data by using the device ID for an encryption key. Second encryption is applied to the encrypted data by using the media ID for an encryption key resulting in applying double encryption to the data. In the case of reproduction, the media ID is read from the memory card and 1st decoding is applied to the encrypted data. Furthermore, the device ID is read from the device ID memory 11 and 2nd decoding is applied to the data by using the device ID for a decoding key. Since the IDs cannot be rewritten and decoding cannot be executed without using the IDs, even illegally copied data cannot be decoded so as to prevent illegal use of the data.