16. A memory device comprising: a plurality of normal word lines; a redundant word line; and a word line control unit suitable for selectively activating the normal word lines, and replacing a frequently activated word line with the redundant word line when the frequently activated word line is detected among the normal word lines, wherein memory cells coupled to a normal word line adjacent to the redundant word line, among the normal word lines, have a longer retention time than memory cells coupled to a normal word line which is not adjacent to the redundant word line.
16. A memory device comprising: a plurality of normal word lines; a redundant word line; and a word line control unit suitable for selectively activating the normal word lines, and replacing a frequently activated word line with the redundant word line when the frequently activated word line is detected among the normal word lines, wherein memory cells coupled to a normal word line adjacent to the redundant word line, among the normal word lines, have a longer retention time than memory cells coupled to a normal word line which is not adjacent to the redundant word line. 21. The memory device of claim 16 , wherein the word line control unit copies data of memory cells coupled to the frequently activated word line into memory cells coupled to the redundant word line.