PURPOSE: To realize the plotting with high quality, by adding a blur detecting mechanism to a plotting system and performing the replotting to the detected blur part.

CONSTITUTION: The ink flowed out of an ink pen 6 becomes short or causes a blur 12 during the plotting. In this case, the blur 12 of a line 11 is detected by a lens 13 and a detector 7, and the blur detecting state is sent to a control part 2 through a blur detecting circuit 9. The part 2 receives the information and shifts the pen 6 to the startin point of the data that is under plotting to perform the replotting on the plotting line part including the blur 12. At the same time, the occurrence of the blur 12 is displayed on a display device 4.