A semiconductor memory device comprises planes each configured to comprise flag cells storing data about program methods of memory cells of the plane, page buffer units configured to sense the data of the flag cells, a flag cell data detection circuit configured to make a determination of program methods of the planes on the basis of a result, obtained by comparing the sensed data of the flag cells of the planes, and the sensed data of the flag cells, and a microcontroller configured to control the page buffer units, wherein the page buffer units read least significant bit (LSB) data of the planes or both the least significant bit (LSB) data and most significant bit (MSB) data on the basis of the determination of the flag cell data detection circuit.