A semiconductor memory device includes a cell array including a plurality of cell regions, a row decoder configured to drive rows corresponding to cell regions in which a refresh operation is to be performed, based on a counting address, and a refresh address generator configured to generate the counting address and a modified address in response to a control signal, wherein the modified address is generated by inverting at least one bit of the counting address, and wherein the semiconductor memory device performs concurrent refresh operations on a first cell region corresponding to the counting address and a second cell region corresponding to the modified address where the second cell region is determined to have weak cells.