Herein disclosed is a graphic data processing system comprising: an image memory (l2) for storing a character pattern as font data composed of binary informations and for displaying the graphic data of the character pattern; first and second color registers (l407, l408) for holding color informations corresponding respectively to the "O" and "l" signals of the font data stored in the image memory (l2); data extending means (l402, l4l5) for ex­tending the one bit of the font data, which are stored in the image memory (l2), for one word into n bits on the basis of the bit number n composing one pixel; a multi­plexer (l409) for multiplexing the color informations, which are latched in the first and second color registers (l407, l408), independently at respectively corresponding bit units on the basis of the data extended by the data extending means; and means (l4l0) for masking and writing the data of the one word, which are multiplexed by the multiplexer, as the graphic data at the bit units in the image memory, whereby a plurality of pixels in one word are processed simultaneously in parallel.