To provide a segment plotting device capable of speeding up plotting processing as a whool by calculating an incremental coefficient at high speed at the time of plotting a segment in a DDA(digital deferential analyzer) system.

This device is provided with a set-up processing means 10 for calculating the length of a segment to be plotted and the incremental coefficient value of the segment and a DDA processing means 4 for operating DDA processing based on the incremental value calculated by the set-up processing means 10. In this case, the set-up processing means 10 outputs the incremental coefficient value having calculating precision decided according to the segment length to a DDA processing means 4.