A device for decoding input data including first candidate data and second candidate data by using a polar code, the device includes a first path metric processor configured to generate first candidate path metrics based on a first parent path metric by decoding the first candidate data, determine at least one first child path metric among the first candidate path metrics based on first reliability values of the first candidate path metrics; and a second path metric processor configured to generate second candidate path metrics based on a second parent path metric by decoding the second candidate data, and determine at least one second child path metric among the second candidate path metrics based on second reliability values of the second candidate path metrics, a quantity of the at least one first child path metric being different from a quantity of the at least one second child path metric.