Disclosed is a method by which a transmission terminal transmits a signal by using device-to-device direct communication in a wireless communication system. Particularly, the method comprises the steps of: identifying each of a plurality of resource units as a clean unit or a dirty unit; selecting one of the clean units as a transmission resource if the number of clean units is a first threshold value or more; selecting, as the transmission resource, one among the one or more dirty units from which interference that is a second critical value or more is detected if the number of clean units is less than the first threshold value; and transmitting a device-to-device direct communication signal by using the selected transmission resource.