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. 22. The memory device of claim 16 , wherein when data of memory cells coupled to the frequently activated word line are copied into memory cells coupled to the redundant word line, the word line control unit activates the redundant word line when the frequently activated word line is activated.