PURPOSE: To realize the copying of the pattern displayed at part on the viewer to another area on the viewer by securing a processable constitution independently for the copying function.

CONSTITUTION: Copying control circuit 40 receives vertical and horizontal address data Vi and Hi to produce new addresses Vi' and Hi' each. Among the process functions of circuit 40 to perform the address conversion, the address designation of the copying destination is carried out via address bus AB and data buss DB. Bus AB performs the register designation within circuit 40, and bus DB performs designation for the data to be set to the designated register. To secure the square area for the copying destination, two registers are used for the upper left start point and the right lower finish point of the area. Thus the vertical and horizontal addresses of refresh memory 34 are converted temporarily in circuit 40, and the vertical and horizontal addresses on the viewer plus that of the refresh memory are defined as copying destination area 22 each to obtain the display state as shown in Fig. b.