Memory device and a semiconductor device

PROBLEM TO BE SOLVED: To provide a storage device capable of achieving low power consumption while suppressing reduction in the operation speed.SOLUTION: A storage device includes: a first transistor 11; a second transistor 12 that controls the supply of a first signal to a gate which is included in the first transistor 11; a logic element 13 that, when a second signal that is input changes from a first potential to a second potential that is lower than the first potential, changes either one of a source and drain of the first transistor from the second potential to a third potential that is lower than the second potential, and then changes it from the third potential to the first potential; and a semiconductor element 16 that has a function of setting the other of the source and drain of the first transistor 11 to a floating state. The first transistor 11 has a channel formation region in an oxide semiconductor film.