In a wireless communication system, user equipment (UE) can reselect a sidelink resource used for vehicle-to-everything (V2X) communication. Reselection of a sidelink resource may be triggered by various conditions, and especially can be triggered when one or more resource pools are configured by an upper layer. In particular, the user equipment determines that data for V2X is present in a sidelink traffic channel (STCH), determines that the one or more resource pools are configured by the upper layer, and reselects the sidelink resource.