1. A semiconductor memory device with NAND strings arranged therein, the NAND string having a plurality of electrically rewritable and non-volatile memory cells connected in series, comprising: a first data area; and a second data area, which is smaller in capacity than the first data area and random accessible at a higher rate than the first data area, wherein the first data area is sequentially accessed in such a way that a sector defined by a certain number of bits serves as an access unit, and the second data area has a word line length shorter than that of the first data area.