A second conductor, third conductor, and fourth conductor sandwiches a first layer together with a first semiconductor. The fourth conductor is positioned farther from the first conductor than the third conductor, which is positioned farther from first conductor than the second conductor. A first circuit is configured to apply a first potential to the first and second conductors, apply a second potential lower than the first potential to the third conductor in parallel with the application of the first potential, and apply a third potential higher than the second potential and lower than the first potential to the fourth conductor in parallel with the application of the first potential.