The present invention adopts a configuration making a decision on a half-tone dot image focused on cyclicity of an image of a half-tone dot decision information adding circuit 102 on an image input from an image reader 101 in advance, adding the decision result to the image as half-tone dot decision information and carrying out various kinds of image processing using the image data in an arbitrary order. Image processing blocks 103, 104 and 105 store added half-tone dot decision information and transmit the half-tone dot decision information to the next block. The scaling circuit 104 is constructed in such a way as to decide, in the case of scale-up, half-tone dot decision information scaled up based on the output pixel position and half-tone dot decision information before and after the pixel position and decide, in the case of scale-down, half-tone dot decision information scaled down by decision by majority or under an OR condition of the half-tone dot decision information within the input pixel range corresponding to one pixel output.