A method of establishing a connection with a network by a relay user equipment, UE, having a connection to a remote UE in a wireless communication system, the method comprising: receiving a relay request from the remote UE; transmitting a random access preamble to a base station, BS, after receiving the relay request; receiving a random access response in response to the random access preamble; transmitting a radio resource control, RRC, connection request message after receiving the random access response; and transmitting an RRC connection setup complete message after receiving an RRC connection setup message in response to the RRC connection request message, wherein if the relay UE does not need to request a connection for traffic of the relay UE, an establishment cause included in the RRC connection request message is configured based on information provided by the remote UE and the RRC connection setup complete message includes an establishment cause configured for use in a relay operation of the relay UE, characterized by: wherein if the relay UE needs to request the connection for the traffic of the relay UE, the RRC connection request message includes an establishment cause having a higher priority between the establishment cause configured for the connection request for the traffic of the relay UE and the establishment cause configured based on the information provided by the remote UE and the RRC connection setup complete message includes an establishment cause having a lower priority between the establishment cause configured for the connection request for the traffic of the relay UE and the establishment cause configured based on the information provided by the remote UE. receiving a relay request from the remote UE; transmitting a random access preamble to a base station, BS, after receiving the relay request; receiving a random access response in response to the random access preamble; transmitting a radio resource control, RRC, connection request message after receiving the random access response; and transmitting an RRC connection setup complete message after receiving an RRC connection setup message in response to the RRC connection request message, wherein if the relay UE does not need to request a connection for traffic of the relay UE, an establishment cause included in the RRC connection request message is configured based on information provided by the remote UE and the RRC connection setup complete message includes an establishment cause configured for use in a relay operation of the relay UE, characterized by: wherein if the relay UE needs to request the connection for the traffic of the relay UE, the RRC connection request message includes an establishment cause having a higher priority between the establishment cause configured for the connection request for the traffic of the relay UE and the establishment cause configured based on the information provided by the remote UE and the RRC connection setup complete message includes an establishment cause having a lower priority between the establishment cause configured for the connection request for the traffic of the relay UE and the establishment cause configured based on the information provided by the remote UE.