A memory device according to this invention includes: N internal memory read buses and N internal memory write buses each including a plurality of internal slots; N memory modules; an output data bus and an input data bus each including a plurality of external slots; a read data processing unit which (i) selects, from pieces of data read from the N memory modules via the N internal memory read buses, pieces of data read via two or more internal slots, and (ii) provides the selected pieces of data to external slots of the output data bus; and a write data processing unit which provides each of pieces of data provided via the external slots included in the input data bus, to one of the internal slots included in the N internal memory write buses, so as to write the pieces of data to the N memory modules.