PURPOSE: Not only to reduce the load of software but to shorten the transfer timer, by using a key input buffer and a screen memory in common under the control of a direct memory access controller.

CONSTITUTION: The 1-frame parameter of a CRT screen is analyzed by a parameter analyzing circuit 18, and the strobe signal delivered while a key input device 11 is operated is detected by an R-S type FF13. Then a request signal for direct memory access DMA transfer is delivered. The information supplied with key by the request signal of the FF13 is supplied to a screen/key input buffer memory 15 from a DMA controller 16 based on the information obtained by the circuit 18. Then the input data is transferred to the memory 15, and the same time a CRT controller 19 is controlled to reset an R-S type FF17 when the DMA transfer of data has been completed. Then an error signal to the operation of key carried out after the end of the DMA transfer of data is delivered to a CPU.