A normally-off state of an OS transistor is maintained or an on-state current thereof is increased without additionally generating a positive potential or a negative potential. When data is written to a node connecting an OS transistor and a capacitor, a potential supplied to the other side of the capacitor is set to an L level, and when the data is retained, the potential is switched from the L level to an H level. In addition, a power switch for a volatile memory circuit is provided on a low power supply potential side so that the supply of a power supply voltage can be stopped. Accordingly, at the time of data retention, a source and a drain of the OS transistor can be set at a high potential, whereby the normally-off state can be maintained and the on-state current can be increased.