An image processing device has an image memory for storing image data, a semi-automatically trace processing for tracing line images of the image data by entering a trace starting point of the image data and an instruction to start tracing, and a display input unit for giving an instruction to enter on a display screen, thereby starting tracing the line images of the image data from the trace starting point thereof. In the method for entering the trace starting points, the image of the image data to be traced is displayed on the display screen through the display input unit, a line segment for specifying the trace starting points thereof is entered so as to intersect the line image displayed on the display screen, an intersecting point at which the line segment therefor intersects the line image is determined, and the resulting intersecting point is entered as a trace starting point, together with an instruction to start tracing.