PURPOSE: To allow a host to access a bit map memory without being conscious of a boundary between upper and lower picture memories by preparing a register for setting up the center address of a display and an address conversion part.

CONSTITUTION: At the time of receiving an access address from an address bus 6, the address conversion part 4 compares the received address with a center address value stored in the register 3, and when the access address is less than the center address value, generates a selection signal 9 for driving an upper side memory block 1 and supplies the inputted access address to a memory block 1 as it is to execute reading/writing access operation. When the access address is more than the center address value, the conversion part 4 outputs a selection signal 10 for driving a lower side memory block 2 and supplies a difference between the inputted access address and the center address value as the address of the memory block 2 to execute access operation.