PURPOSE: To execute a designation of a wide ROM area by constituting so that a selector designates a prescribed bank register irrespective of the contents of a bank register group selecting signal, when a bank register selecting signal for showing a prescribed value is supplied to the selector.

CONSTITUTION: A selector 3b designates a bank register group of a symbol "0" when a bank register group selecting signal supplied from an address register 5 is "0", also designates a bank register of (a) when a bank register selecting signal supplied from an ROM 2 is "0", and designates a bank register of (b) when a bank register selecting signal is "01". Thereafter, the designation is executed in the same way. As for these designated bank registers, the storage part is designated when an address signal is supplied through an address decoder from the ROM 2. As a result, an RAM area can be widened without lengthening a cord of the ROM, and also a data can be transferred only between RAM areas.