A refresh method for a semiconductor memory device features high noise resistance, lower power consumption, and lower cost. All word lines of one or more memory cell blocks that have not been selected in a self refresh mode are controlled to have a floating potential substantially at ground level. Even when a word line and a bit line are short-circuited, this control prevents destruction of memory cell information, which may be caused by noise, and also prevents generation of leakage current. A fuse, etc., for preventing generation of leakage current is unnecessary, so that lower cost is realized.