The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for triggering a sidelink buffer status reporting in a D2D communication system, the method comprising: configuring a first ProSe destination including at least one first UE and a second ProSe destination including at least one second UE; receiving a first sidelink data for a first sidelink logical channel from an upper layer; receiving a second sidelink data for a second sidelink logical channel from the upper layer while the UE has the first sidelink data for the first logical channel, wherein the second logical channel has a higher priority than a priority of the first sidelink logical channel; and triggering a buffer status reporting the if the first sidelink logical channel and the second sidelink logical channel belong to a same ProSe destination.