When an internal storage device or an output device does not have a sufficient free space, predetermined part of the unstored subject data in an external storage device is stored into the internal storage device; the subject data having been stored in the internal storage device is output then the area where the subject data is stored in the internal storage device is released. When the internal storage device has a free space in which all the unstored subject data can be stored, all the unstored subject data is stored into the internal storage device; a communication condition between the communication unit and the external storage device is detected; and the subject data is output except for at least part of the subject data to be output lastly. The subject data is output only when the communication condition has been changed to the non-communicatable condition.