A device for allocating a channel by using wireless access in a vehicular environment in which an onboard unit is provided in a vehicle and at least one roadside unit is provided, receives a service announcement message from at least one roadside unit, uses the service announcement message to generate an available service table, determines whether the available service table has roadside unit entries for transmitting the service announcement message, and if so, compares average RSSI provided by the roadside units to select a roadside unit to access, selects a channel that corresponds to the service provider ID with the highest priority from among the service provided by the selected roadside unit, and assigns the selected channel as a service channel to exchange information with the roadside unit.