To provide a memory structure of a on-screen display device capable of changing a display parameter for every line in one and the same screen page, and optimizing the memory space according to the application.

In the device to control the display of letters in a video system, a memory to store the information on the display of the letters is divided into two areas. The first area (Z1, Z1') is of fixed address, and stores the information and the data for the general control of the display. The second area can be divided into spaces (B1, B2, B3) of variable size, and each space stores the control parameters and the data related to the display of the lines of the letters. The spaces are connected to each other by the parameters stored in each to indicate the address of the next memory space. The memory structure can change the display parameters for every line in one and the same screen, and optimize the size of the memory to be used.