A CPU determines whether the intended use of the image data to be stored in a plurality of HDDs has a first-type purpose, which requires storing temporarily stored image data for carrying out output processing of the image data, or a second-type purpose, which requires long-term preservation of the image data. If the first-type intended use is determined, a first-type mode for saving is selected, wherein the image data to be stored are divided and each divided set of image data is stored into one HDD. If the second-type intended use is determined, a second-type mode for saving is selected, wherein the same image data part is saved in a plurality of storage means.