A memory system includes a memory including nonvolatile memory cells, and a controller configured to set read voltages for reading data stored in the nonvolatile memory cells. The controller stores first shift patterns relating to a plurality of read voltages, first index information associating to a first shift pattern with each of a plurality of memory cell groups, second shift patterns relating to differences between read voltages and read voltages set according to a first shift pattern, and second index information associating a second shift pattern with each memory cell group. The controller generates read voltages of a target memory cell group based on the first shift pattern voltages and the second shift pattern voltages.