A storage device able to make a redundant write operation of unselected data unnecessary and able to optimize an arrangement of pages to a state having a high efficiency for rewriting, wherein the storage device has a first memory unit, a second memory unit having a different access speed from the first memory, and a control circuit, wherein the control circuit has a function of timely moving the stored data in two ways between the first memory unit and the second memory unit having different access speeds in reading or rewriting.