It is an object of the present invention to provide an image processing device for allowing an actual-image-closer pattern to be formed based on the design data, or its simulation image. In order to accomplish the above-described object, the proposal is made concerning an image processing device which includes an image processing unit which sets the operation condition of a charged-particle beam device on the basis of the design data on a semiconductor element. Here, the image processing device accesses a library for storing device-condition information on the charged-particle beam device, pattern types, and a plurality of combinations of pattern information on each pattern-region basis. Moreover, the image processing device forms a composite image of each pattern region, using the pattern information on each pattern-region basis, and based on the device-condition information and the selection of a pattern type from the pattern types.