It is an object to obtain a memory element (DRAM) storing multilevel data easily. The amount of charge accumulated in a capacitor of a memory element (DRAM) is controlled by changing the potential of a wiring (a bit line), which is used for writing data to the memory element (DRAM), in a period in which a transistor included in the memory element (DRAM) is on. Thus, multilevel data stored in the memory element (DRAM) can be obtained without a complex configuration of a semiconductor device including the memory element (DRAM).