A temporary storage circuit including a reduced number of transistors is provided. The temporary storage circuit includes storage elements, each of which includes a first transistor and a second transistor. A channel of the first transistor is formed in an oxide semiconductor layer. A signal potential corresponding to data is input to a gate of the second transistor through the first transistor which is turned on by a control signal input to a gate of the first transistor. Then, the first transistor is turned off by a control signal input to the gate of the first transistor, so that the signal potential is held in the gate of the second transistor. When one of a source and a drain of the second transistor is set to a first potential, the state between the source and the drain of the second transistor is detected, whereby the data is read out.