This device includes an image data creator that creates a first type of image data for test shooting and creating a second type of image data for real shooting; a compressor that compresses the image data in a predetermined compression format; and a processor; wherein the compressor has one or plural compression parameters relating to a compression rate; the creator newly supplies files of the first type to the compressor one after another; the compressor compresses at least two files among the continuously supplied first type using values of compression parameters; the processor decides the value of the compression parameter to be used for the second type according to a predetermined standard, based on two and more files of first type image data that are compressed using values of compression parameters; and the processor sets the value of the compression parameter of the compressor at the decided value.