in accordance with a write address successively updated in synchronism with a dot clock , color display data is written into a memory . the memory includes three memory corresponding to three primary colors and having identical addresses thereto assigned . for the purpose of color display , the written display data is read out three times consecutively during one write clock interval . a read address generator for supplying a read address successively changed to the memory is reset when addresses have been generated up to the number of horizontal display dots . the resetting is performed when the number of horizontal display dots detected from the dot clock and a display timing signal has coincided with a read address signal outputted from the read address generator . since the reset timing of the read address generator changes according to the number of horizontal display dots detected by horizontal display dot number detector , it is possible to cope with a change of the personal computer supplying input data without changing the circuit .