from the alpha blending computing unit 10 as one input image information further as the other input image information the alpha value u03b1 c and pixel value c c of the image c are input as apparent from the above expression 7 the alpha blending computing unit 20 1 outputs the alpha value u03b1 abc of the composite image obtained by synthesizing the images a b and c based on the alpha value u03b1 ab of the composite image output from the alpha blending computing unit 10 and the alpha value u03b1 c of the image c further as apparent from the above expression 8 the alpha blending computing unit 20 1 outputs the alpha multiplied pixel value u03b1 abc c abc of the composite image of the images a b and c based on the alpha multiplied pixel value u03b1 ab c ab of the composite image output from the alpha blending computing unit 10 and the alpha value u03b1 c and pixel value c c of the image c that is in the case of generating an alpha multiplied pixel value u03b1c to be output the alpha blending computing unit 20 1 uses an alpha multiplied pixel value out of input image information and does not take an alpha value corresponding to the alpha multiplied pixel value into consideration thus the alpha multiplied pixel value u03b1c output from the alpha blending computing unit at the previous stage can be directly received this makes it possible to dispense with a divider that needs to be provided between tandem connected alpha blending.