1. A printer, comprising: an input unit configured to input RAW data and image data of a general-purpose format; an image generating unit configured to generate a generated image of a general-purpose format from RAW data input by the input unit using a demosaicking processing; a print unit configured to print the generated image and configured to print images generated from image data of a general-purpose format input by the input unit; and a storage unit that stores the generated image into an external storage medium as a stored image, wherein the print unit prints the stored image and the storage unit checks the external storage medium for the free capacity thereof and, when the external storage medium is short of the capacity for storing the generated image, requests a user to add another external storage medium.