An image synthesizing device includes a graphics data expanding unit 2 for securing a rectangular area 4a whose alpha value is “0” in a region of a non-display memory 4, the region corresponding to a display area in which moving image data is to be displayed, and for expanding motionless graphics data onto a region of the non-display memory 4, the region corresponding to a display area in which the motionless graphics data is to be displayed, and a moving image data expanding unit 3 for expanding the moving image data onto a non-display memory 5. The image synthesizing device then synthesizes the graphics data which are expanded onto the non-display memory 4 and the graphics data which are expanded onto the non-display memory 5.