1. A decoding method comprising: performing a first decoding method comprising updating a plurality of variable nodes and a plurality of check nodes using probability values of received data; and performing a second decoding method when decoding of the first decoding method fails, wherein the second decoding method comprises: selecting at least one variable node from among the plurality of variable nodes; correcting probability values of data received in the selected at least one variable node; updating the variable nodes and the check nodes using the corrected probability values; and determining whether decoding of the second decoding method is successful, wherein selecting the at least one variable node comprises: when the updating is performed a plurality of times, counting the number of unsatisfied check nodes at each update time; and selecting the at least one variable node from among the variable nodes connected to unsatisfied check nodes corresponding to at least one update time having the minimum counted number of unsatisfied check nodes.