In a nonvolatile memory apparatus, a system bus receives address, command, and/or control signals. Memory cells store bits of data by shifting a threshold voltage to one of plural ranges. In writing a first page, the threshold voltage of a first memory cell remains in a first range or shifts into a second range. In writing a second page, the threshold voltage remains in the first or second voltages, or shifts into a third range from the first range or into a fourth range from the second range. Before writing the second page, the memory reads data from the first memory cell for generating the second page writing data. A shifting direction of the threshold voltage from the first to the second range is the same as a shifting direction from the first to the third range.