A backup system (100) installed in an airplane comprises a controller (130), storages (140, 150), a detector (120), and an input apparatus (180). The first storage (140) stores a large amount of data needing to be backed up, such as software for on-board equipment and usage information for an entertainment apparatus (160) and a payment apparatus (170). Based on information from the detector (120) and the input apparatus (180), the controller (130) determines/predicts a transition to stable flight and determines a timing at which a backup operation will be carried out. In addition, an interruption of stable flight is predicted/determined and a backup process is interrupted. A priority is decided for each piece of data to be backed up, and a backup order is decided based on the priority. The backup system (100) predicts sections in which stable flight will be possible from meteorological information, etc., and performs backup.