The object of the present invention is to assign line break numbers to locations where line breaks have been made in order to separate a series of figures configured by connecting a number of figures into parts in a manner which makes it easy for a user to view a drawing including the series of figures, or a series of figures. In response to a line break operation for separating a series of figures configured by connecting a plurality of figures into parts, line break numbers displayed at line break locations are sorted based on a positional relationship of the line break locations. The series of figures with the sorted line break numbers assigned to the line break locations is displayed after performing the line break operation. The line numbers are therefore assigned in a consecutive manner for each series of figures. If there are a plurality of series of figures within a drawing, the line break numbers are assigned to the series of figures using a predetermined rule so that the drawing as a whole becomes easier to see.