The present invention relates to a wireless communication system. Particularly, the present invention relates to a method and device by which a terminal performs a discovery step for D2D communication in a wireless communication system, the method comprising the steps of: receiving a first discovery signal (DS) including identification information of a target terminal from a member terminal of a first terminal group; checking whether the target terminal belongs to the first terminal group; and transmitting a second DS corresponding to the first DS, wherein if the target terminal belongs to the first terminal group, the second DS is transmitted to member terminals within the first terminal group, and if the target terminal does not belong to the first terminal group, the second DS is transmitted to a specific terminal within a second group different from the first group.