1. An image file sorting method executed by an image file sorting device, wherein the image file sorting device includes a storage unit, a control unit, and an image reading unit, and the storage unit includes a sorting condition storage unit that stores, as a sorting condition to specify a sorting destination of an image file, a type of border line including solid line and broken line drawn in a marker portion of the image file, the method comprising: a sorting keyword extracting step of recognizing the type of border line including solid line and broken line drawn in the marker portion of the image file read by the image reading unit, and extracting the type of border line as a sorting keyword; a sorting destination deciding step of deciding the sorting destination of the image file by collating the sorting keyword extracted based on the type of border line at the sorting keyword extracting step with the sorting condition stored in the sorting condition storage unit; an image file sorting step of sorting the image file into the sorting destination decided at the sorting destination deciding step; and a sorting condition updating step of detecting property information of the image file sorted into the sorting destination at the image file sorting step, and when the detected property information is recognized as new property information, updating the sorting condition based on the new property information to store the sorting condition in the sorting condition storage unit; wherein when the detected property information is recognized as new property information, automatically updating the sorting condition based on the new property information to store the sorting condition in the sorting condition storage unit.