It is an object of this invention to provide an image processing device which would be able to extract a specified pattern accurately even if there are fine lines in its periphery. The invention is configured as follows in order to achieve this object. The density data for R, G and B are transmitted to fine line processor. There a count is made of the number of pixels among the eight surrounding a center object pixel, which have density values within a fixed margin of the center object pixel. If there are three or fewer, the center object pixel is judged to be part of a line segment, and the determination flag 0 is output. If there are four or more, the center pixel is judged to be not part of a line segment, but a part of pattern. Once the object pixel is judged to be a part of a line segment, then a line removal device remove the object pixel from the image data in order to extract a specified pattern.