A memory system performs a first sensing operation to sense whether multi-level cells assume an on-cell state or an off-cell state in response to a first read voltage applied to a selected word line. It then supplies a pre-charge voltage to bit lines corresponding to multi-level cells that have been sensed as assuming the off-cell state in response to the first read voltage, and it performs a second sensing operation with the supplied pre-charge voltage to sense whether each of the multi-level cells that have been sensed as assuming the off-cell state assumes an on-cell state or an off-cell state in response to a second read voltage applied to the selected word line.