A disclosure of the present specification provides a method for selecting, by a user equipment (UE) located outside a coverage of a base station, a neighboring UE with which the UE will perform device-to-device (D2D) communication. According to the method, it is possible to quickly find out whether a neighboring UE is located within the coverage of a base station and is capable of operating as a relay, through a DMRS and a detection signal received from the neighboring UE.