The present invention relates to a reading method of a memory device including a memory cell including a first or N program state and a removing state comprising: a step of determining first reading power of the first program state and the removing state based on the distribution change of the first program state and the distribution change of the removing state; and a step of determining the other reading power among the second or the N reading power based on the one reading power by determining the one reading power among the second or the N reading power based on the distribution change of two program states among the first or the N program state. N is bigger than 3 and is a natural number. [Reference numerals] (S310) Determining first read voltage based on the distribution change of a first program state and a removal state; (S320) Determining second or N read voltage based on one or more distribution changes among first or N program states
