The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for initiating a random access procedure in a carrier aggregation system, the method comprising: receiving, from a network, a Radio Resource Control (RRC) signal which configures a Physical Uplink Control Channel (PUCCH) resource for an cell in a Timing Advance Group (TAG); initiating a dedicated random access procedure on the cell with the PUCCH resource to be configured by the RRC signal if the RRC signal includes a dedicated random access preamble information for the cell.