In a semiconductor layer, information is written by applying a first potential to a first electrode, applying a second potential that is lower than the first potential to all of back gate electrodes, applying a third potential that is higher than the first potential to the first to (i−1)th front gate electrodes, and applying a fourth potential that is between the second and third potentials to the ith and subsequent front gate electrodes, where “i” is a positive integer and identifies a specific location to which information is to be written.