When a list of file names is to be displayed on a display device, a comparison is made between a necessary display width of each of the file names and a width of a display area of the display device. For each of the file names having a necessary display width greater than the width of the display area, it is checked whether the file name contains a particular character string portion of a predetermined type, and, if so, the file name is displayed in the list in a partly-omitted display style where a leading end portion, particular character string portion and extension of the file name are left in the list with the other part of the character string omitted. The particular character string portion can function as an important element for identifying the data item in question.