According to one embodiment of the present invention, a method of selecting a synchronization source, which is selected by a D2D (device-to-device) UE in a wireless communication system includes the steps of receiving a plurality of synchronization signals, selecting a plurality of candidate synchronization signals from a plurality of the synchronization signals and determining a synchronization signal in a manner of applying a priority to a plurality of the candidate synchronization signals and selecting a UE, which has transmitted the determined synchronization signal, as a synchronization source. In this case, the application of the priority can be performed in a manner of sequentially applying a plurality of priorities related to a D2D signal according to a priority for the application of the priority.