In one aspect, a program method is provided for a flash memory device including a plurality of memory cells each being programmed in one of a plurality of data states. The program method of this aspect includes programming selected memory cells in a first data state, verifying a result of the programming, successively programming selected memory cells in at least two or more data states corresponding to threshold voltages which are lower than a threshold voltage corresponding to the first data state, and verifying results of the successive programming.