An object is to prevent an operation defect and to reduce an influence of fluctuation in threshold voltage of a field-effect transistor. A field-effect transistor, a switch, and a capacitor are provided. The field-effect transistor includes a first gate and a second gate which overlap with each other with a channel formation region therebetween, and the threshold voltage of the field-effect transistor varies depending on the potential of the second gate. The switch has a function of determining whether electrical connection between one of a source and a drain of the field-effect transistor and the second gate of the field-effect transistor is established. The capacitor has a function of holding a voltage between the second gate of the field-effect transistor and the other of the source and the drain of the field-effect transistor.