A method is for programming a flash memory device which includes a plurality of memory cells storing multi-bit data representing one of a plurality of states. The method includes programming the multi-bit data into selected memory cells of the plurality of memory cells, the programming including a first verify-reading operation performed by a first verifying voltage, determining whether to execute a reprogramming operation for each of the selected memory cells, and reprogramming the selected memory cells in accordance with the determination. The reprogramming of the selected memory cells includes a second verify-reading operation performed by a second verifying voltage, the second verifying voltage being higher than the first verifying voltage.