PURPOSE: To simplify handling trouble in a raster/vector simultaneous editing operation and to improve operation efficiency by automatizing a raster data deletion processing after preparing vector data.

CONSTITUTION: An operator operates a keyboard 1 and a mouse 2 and inputs a line segment vector data preparation instruction and coordinate data. Then, after a prescribed preprocessing, a raster data deletion part 11 deletes raster data based on line width information supplied from a deletion line width storage part 10 and updates the raster data inside a raster data storage part 14. A vector data preparation part 13 prepares line part vector data supplied with line width based on preparation vector line width information supplied from a vector line width storage part 12 on the deleted raster data and updates the line segment vector data of a vector data storage part 15. The updated respective raster data and the line segment vector data are displayed on a display device 16. Thus, the useless raster data are automatically deleted.