Provided is a method for declaring a radio link failure (RLF) by a radio resource control (RRC) layer of a user equipment (UE). The method may include: receiving information on failure of beam recovery, from a lower layer of the UE; receiving at least one out-of-sync (OOS) signal, from the lower layer of the UE; and when a number of OOS signals which is received after receiving the information on failure of beam recovery satisfies a threshold value, declaring the RLF.