A semiconductor memory device includes a memory cell array to which a plurality of word lines are coupled, a voltage generation circuit configured to apply operating voltages to the plurality of word lines during a program operation, and a control logic configured to control the voltage generation circuit to perform a discharge operation for the plurality of word lines when an external power supply voltage is reduced during the program operation, wherein the control logic controls the voltage generation circuit such that, during the discharge operation, a potential level of a selected word line among the plurality of word lines is discharged, and then potential levels of the other unselected word lines are discharged.