1. A line drawing image generating device for generating line drawing data based on original image data, comprising: ink line area detecting means for detecting an area whose brightness is smaller than a predetermined value in an original image, as an ink line area; neighboring area detecting means for detecting a neighboring area of the ink line area, which surrounds the ink line area; outline area detecting means for detecting an outline portion of an image as an outline area, with respect to an area other than the ink line area and the neighboring area in the original image; line drawing data storing means for storing the line drawing data; and color data writing means for writing color data to a storage area of the line drawing data storing means, which corresponds to the ink line area and the outline area, and writing different color data to a storage area of the line drawing data storing means, which corresponds to an area other than the ink line area and the outline area.