The present invention relates to a method and apparatus for operating a soft buffer for device-to-device (D2D) communication and eNode B-to-device (E2D) communication of a terminal in a wireless communication system. Specifically, the present invention comprises the steps of: receiving D2D communication data; and storing the D2D communication data in a soft buffer of a specific downlink hybrid automatic repeat and request (HARQ) process, wherein the specific downlink HARQ process is configured to support D2D communication among a plurality of downlink HARQ processes configured for E2D communication, and the step of storing the D2D communication data comprises: when E2D data are already stored in all soft buffer areas associated with the plurality of downlink HARQ processes, discarding the E2D data already stored in the soft buffer area of the specific downlink HARQ process and storing the D2D communication data therein.