Non volatile memory device and operating metho thereof

PURPOSE: A non volatile memory device and operating method thereof are provided to secure an appropriate read margin suitable by varying a read voltage. CONSTITUTION: An encoder(132) performs a scramble operation to minimize the variance between the occurrence of the number 0 and 1 which are included in data inputted from the outside. A DSV(Digital sum value) generator(134) generates DSV indicating the variance between the occurrence of the number 0 and 1 which are included in the encoded input data. A main cell unit of an n page stores input data which is encoded by the encoder. A spare cell unit of the n page stores DSV which is generated in the DSV generator. A read voltage setting unit(138) compares the DSVs from the main cell unit and space cell to determine a read voltage for the n-page.