To provide a memory element that positively utilizes a phenomenon such as a dielectric breakdown, differently from a conventional memory element, and to provide a memory device having an increased memory capacity. The invention provides a memory device having a pair of electrodes and multiple memory material layers stacked between the electrodes, and an operating method thereof, where the memory material layers are sequentially destroyed by applying voltage. For example, in the case of stacking two memory material layers in the memory device, the memory device is operated in such a manner that a first voltage is applied to the pair of electrodes to destroy one of the two memory material layers, and then a second voltage is applied thereto to destroy the other of the two memory material layers.