Abstract: A drawing assistance device acquires image data of a design diagram to detect dimensional information drawn on the image data, detects arrows drawn on the image data, detects a line drawn on the image data, combines the arrows and the line based on positions of the arrows and a position of the line to generate a dimension line, detects a dimension value corresponding to a position of the dimension line from the dimensional information so as to assign the detected dimension value to the dimension line, generates guidelines indicating positions of ends of the dimension line, superposes the guidelines on the image data to display the guidelines on an editing screen, and outputs digital data of the design diagram drawn by the operator on the editing screen on which the guidelines are displayed.