In a wireless communication system comprising at least one user equipment (UE) and a plurality of devices using the same wireless network used by the at least one UE, a base station determines whether congestion has occurred on a random access channel (RACH) due to random access by the plurality of devices, modifies system information so as to reduce the number of UEs using one preamble from preambles that belong to a first preamble group, when congestion has occurred on the RACH, and broadcasts the system information that is modified, wherein the first preamble group from a plurality of preamble groups comprises preambles that are used by the plurality of devices.