Note that the present example is explained on the assumption that the normal word line WLi?1 or WLi+1 is not defective, and, therefore, replacement by the redundant word line RWL is not carried out. Therefore, also in the third target-row refresh operation, the hit signals HIT0 to HITm are not activated.

As a result, the row predecoder 41 and the row decoder 42 select the normal word line WLi?1 or WLi+1 adjacent to the other side of the normal word line WLi indicated by the target address input from outside, and the normal memory cells MC connected thereto are refreshed. Then, when a precharge command PRE is issued, all of the state signals TRRST1 to TRRST3 are changed to the low level (time t17).

The third target-row refresh operation is completed as described above. In this manner, in the third target-row refresh operation, the normal word line WLi?1 or WLi+1 adjacent to the other side of the normal line WLi indicated by the target address is selected.

In this manner, in the case 1, the normal word line WLi indicated by the target address, the normal word line WLi+1 adjacent to the one side of the normal word line WLi, and the normal word line WLi+1 adjacent to the other side of the normal word line WLi are sequentially selected. As a result, the reduced information retention time are recovered.

Note that the above described example is explained on the assumption that the normal word lines WLi?1 and WLi+1 are not defective. However, if the normal word line WLi?1 or WLi+1 is defective and replaced by the redundant word line RWL, the redundant word line RWL of a replacement destination is selected in the third target-row refresh operation. However, this operation is not essential.

[Case 2 (Number 1)]