An addressing device and method is provided to enable an electronic system having a less addressing capability to address a memory device having a larger storage space, thereby reducing the manufacture cost of the electronic system. The addressing device includes an address decoder and an address translator. The address decoder receives a first access address belonging to a smaller address space, and determines whether to map the first access address to the larger storage space of the memory device. The address translator is coupled to the address decoder. When the first access address is mapped to the storage space of the memory device, the address translator translates the first access address into a second access address of the larger storage space according to an adjustable base address.