A base station apparatus to be used for a mobile communication system capable of providing communications using plural frequency carriers is disclosed. The base station apparatus includes a frequency carrier selection unit selecting one of a first frequency carrier and a second frequency carrier as a frequency carrier to be used for the communications based on at least one of a service type of the communications and a congestion degree of the communications, the first frequency carrier being used for communications based on allocation in which radio resources are dynamically allocated, the second frequency carrier being used for communications based on allocation in which the radio resources are allocated at every predetermined period.