PURPOSE: To accelerate optionally plural making of a transparent color and rewrite of the transparent color in superimposition of plural pictures in a display controller used for navigation system, etc.

CONSTITUTION: Display data color address signals a1, a2 are read out from first and second memories 1, 2 successively by the controller 7 to be converted into corresponding color signals b1, b2 for display data by first and second color palettes 3, 4. These signals are inputted to a selector 5, and a color signal (D) for synthesis display data as the result of superimpose of the display data is obtained by a selector selection signal (c) from the first color palette 3 to be displayed on a display device 6. By giving not only color information for first display data to the first color palette 3, but also the information as the selector selection signal (c) at every color address, plural transparent colors of the first display data projecting the second display data are taken simultaneously, and the number and the combination are changed freely, and the rewire of the transparent color specification is accelerated also.