FIG. 19 is a second timing chart for explaining the target-row refresh operations in the case 2. Herein, in the case 2, a case in which the redundant word line RWL0 is unused is explained.

The operations corresponding to time t31 to t35 are similar to those of FIG. 18. More specifically, the normal word line WLN is selected in a first target-row refresh operation, and the normal word line WLN?1 is selected in a second target-row refresh operation.

Then, the target address is input in relation to a third target-row refresh operation (time t36). In the present example, since the redundant word line RWL0 is unused, the enable signal AFEN0 corresponding to the fuse set FSET0 is at the low level. As a result, the usage detection signal USE0 maintains the low level. Therefore, forcible address conversion by the address conversion circuit 43 is not carried out. In this case, also in the third target-row refresh operation, the normal word line WLN?1 is selected as well as the second time.

In this manner, if the redundant word line RWL0 is unused in the case 2, the normal word line WLN indicated by the target address and the normal word line WLN?1 adjacent to the one side of the normal word line WLN are sequentially selected, while the redundant word line RWL0 is not selected. As a result, unexpected erroneous operations caused by selecting the unused redundant word line RWL0 are prevented.

[Case 3]