A memory device includes a pass/fail check circuit configured to compare the number of memory cells, which are verified as being a program fail based on a result of verifying program operations of a first group of memory cells of a plurality of memory cells, with a first reference bit number, and to check whether the first group of memory cells is a pass or fail and a control circuit configured to control the pass/fail check circuit to recheck whether the first group of memory cells is the pass or fail based on a second reference bit number smaller than the first reference bit number when the first group of memory cells is found to be the pass based on a result of a pass/fail check operation of the pass/fail check circuit.