Memory cell arrays include a data cell array, a reference cell array and a dummy cell array. First read word lines are connected respectively to the gates of the read selection switches of the data cells. Second read word lines are connected respectively to the gates of the read selection switches of the reference cells. The gates of the read selection switches of the dummy cells are also connected respectively to the first and second read word lines but the dummy cells do not function as memory cells because the read selection switch and the MTJ element are cut apart in each of the dummy cells.