MASK INSPECTING APPARATUS

A pattern forming apparatus for inverting at least one of plural patterns according to numerical design data respectively representing the plural patterns and synthesizing thus inverted pattern with the remainder of the plural patterns, comprises first operation device for attaching a flag of a positive image to the design data of uninverted patterns, and attaching a flag of an inverted image to the design data of inverted patterns, second operation device for handling the entire area of either inverted patterns or uninverted ones among the plural patterns as a single pattern, and attaching a corresponding flag to the design data of the pattern, and image forming device for forming image data of the area according to the data of the second operation device and then forming image data of each pattern according to the data of the first operation device.