A memory controller controls a semiconductor storage device including nonvolatile memory cells. The controller includes a generating circuit, and a selection circuit. The generating circuit generates first data based on a second data. The selection circuit retains a cumulative value whose each digit is a cumulative result in each bit of data which is already written in the memory cells. The selection circuit selects one of the first data. A selected first data has a better average of digits in a sum of each bit of the selected first data and each digit of the cumulative value than an unselected first data. The selection circuit retains the sum concerning the selected first data as the new cumulative value.