Suggested is a novel condition for a media access control (MAC) entity in user equipment (UE) reselecting a sidelink resource in a wireless communication system. The MAC entity of the UE can reselect a sidelink resource when a configured sidelink grant does not satisfy a latency requirement according to ProSe per-packet priority (PPPP). More particularly, configuration is performed by an upper layer so that the MAC entity transmits on the basis of sensing using a resource pool; the MAC entity selects generation of a configured sidelink grant corresponding to transmission of a plurality of MAC protocol data units (PDU); and when data is available in a sidelink traffic channel (STCH) and the configured sidelink grant does not satisfy the latency requirement according to the PPPP, a sidelink resource is reselected.