A low-power storage device is provided. The storage device includes a first transistor, a second transistor, a logic element, and a semiconductor element. The second transistor controls supply of a first signal to a gate of the first transistor. When the potential of a second signal to be input is changed from a first potential into a second potential lower than the first potential, the logic element changes the potential of a first terminal of the first transistor from a third potential lower than the second potential into the first potential after the logic element changes the potential of the first terminal of the first transistor from the second potential into the third potential. The semiconductor element has a function of making a second terminal of the first transistor floating. The first transistor includes a channel formation region in an oxide semiconductor film.