PURPOSE: To display plural images in correct colors even on the display screen of a display whose display colors are limited in number.

CONSTITUTION: When L (L: integer ≥2) images are displayed on the display 27 whose display colors are limited to an optional number (n) (n: integer) by using an LUT(look-up table) 22, (n) optimum candidate colors are selected among a total number Σmi (where mi is added from 1 to mL and mi is the number of colors that each image uses) of colors of the L images and color reduction processing (10) for integrating colors of the respective colors other than the candidate colors into the candidate colors is performed; and color data of the (n) colors obtained by the color reduction processing (10) are stored in the LUT 22 and the L images are displayed on the screen of a display 27 at the same time.