A rotated pattern generating system includes at least a X-direction straight line generator adapted to calculate, a difference in X- and Y-directions between the position of a given dot on a destination coordinate and a position of the next dot to be coordinate transformed. The difference is determined by the difference on the source coordinate between the given dot and the next dot to be transformed and a required rotational angle .theta.. The system further comprises a detector connected to the X-direction straight line generator for discriminating whether or not a residual pattern occurs each time the X-direction straight line generator generates an output, and a dot generator responsive to the output of the detector to generate, when a dot lack is discriminated on the position of the residual pattern the same dot information as that of the dot adjacent to the residual pattern position in the destination coordinate.