An apparatus and a method of detecting a sync signal, the apparatus including a sync determiner selecting an output sync pattern from a candidate sync signal generated by pattern matching in lock and/or unlock modes and selecting one of candidate sync patterns of the candidate sync signal having a cycle synchronizing with a sync cycle as an output sync pattern to generate an output sync signal; and a mode determiner determining a mode based on the candidate sync signal, a mode conversion threshold value, and a selection number of times the candidate sync pattern is selected as the output sync pattern.