An image processing apparatus contains an alpha-blend execution unit and a storage device management unit. The alpha-blend execution unit allocates a memory area in a main memory for an alpha-blend execution to compose transparency properties and carries out the alpha-blend execution in a process to convert a page description language data to an image. The page description language data contains a drawing object having a transparency property and a canvas having a transparency property. The drawing object is drawn on the canvas. The storage device management unit evacuates a memory-image of the canvas in the memory area from the main memory to an auxiliary memory, and reads back the memory-image of the canvas from the auxiliary memory to the main memory when the memory-image of the canvas is required for the alpha-blend execution.