Since power source voltages are different depending on circuits used for devices, a circuit for outputting at least two or more power sources is additionally prepared. An object is to unify outputs of the power source voltages. A transistor using an oxide semiconductor is provided in such a manner that electrical charge is retained in a node where the transistor and a capacitor are electrically connected to each other, a reset signal is applied to a gate of the transistor to switch the states of the transistor from off to on, and the node is reset when the transistor is on. A circuit configuration that generates and utilizes a potential higher than or equal to a potential of a single power source can be achieved.