PURPOSE: To shorten the expansion time of a succeeding page by transferring a bit map for one page to a recording section and expanding bit map data of the succeeding page into a bit map without clearing a bit map memory for the succeeding page after the end of the transfer.

CONSTITUTION: A flag is provided to each address and a flag memory 108 stores the flag and a bit map memory 107 and the flag memory 108 are simultaneously accessed at read and data and fixed data '0' from the bit map memory 107 are selected depending on the content of the flag, and data from the bit map memory 107 are read at video signal transfer and a flag to select the fixed data '0' is written in the flag memory 108.