A base station apparatus for carrying out communications with a mobile station in downlink using an OFDM method is disclosed. The base station apparatus is characterized in that the base station apparatus transmits a first signal and a second signal; a predetermined transmission power of the second signal is set; and the base station apparatus comprises a first transmission power controlling section that controls so that a transmission power per unit frequency band of the first signal is constant; and a frequency resource assignment section that determines a frequency resource to be assigned to the first signal, in accordance with the transmission power of the second signal and the transmission power per unit frequency band of the first signal.