A small base station configured to control a transmission power of a radio signal transmitted by the small base station in a mobile communication network including a general base station forming a predetermined cell and the small base station forming a small cell smaller in size than the predetermined cell, the small base station comprising: a reception power acquisition unit configured to acquire a reception power of a radio signal from one of a different small base station or the general base station, which can be received by the small base station; a determination unit configured to determine one of the different small base station and the general base station which transmits the radio signal acquired by the reception power acquisition unit; a pathloss value calculation unit configured to calculate, when it is determined by the determination unit that the radio signal is transmitted from the different small base station, a pathloss value between the different small base station and the small base station based on a difference between a transmission power of the radio signal from the different small base station and the reception power of the radio signal from the different small base station acquired by the reception power acquisition unit; and a transmission power determination unit configured to determine the transmission power of the radio signal transmitted by the small base station, based on the pathloss value calculated by the pathloss value calculation unit, wherein the transmission power determination unit determines the transmission power of the radio signal transmitted by the small base station based on the reception power of the radio signal from the general base station acquired by the reception power acquisition unit, when it is determined by the determination unit that the radio signal is transmitted from the general base station, and wherein the transmission power determination unit determines, as the transmission power of the radio signal transmitted by the small base station, a transmission power having the smaller value from the transmission power of the radio signal from the small base station determined based on the pathloss value and the transmission power of the radio signal from the small base station determined based on the reception power of the radio signal from the general base station. a reception power acquisition unit configured to acquire a reception power of a radio signal from one of a different small base station or the general base station, which can be received by the small base station; a determination unit configured to determine one of the different small base station and the general base station which transmits the radio signal acquired by the reception power acquisition unit; a pathloss value calculation unit configured to calculate, when it is determined by the determination unit that the radio signal is transmitted from the different small base station, a pathloss value between the different small base station and the small base station based on a difference between a transmission power of the radio signal from the different small base station and the reception power of the radio signal from the different small base station acquired by the reception power acquisition unit; and a transmission power determination unit configured to determine the transmission power of the radio signal transmitted by the small base station, based on the pathloss value calculated by the pathloss value calculation unit, wherein the transmission power determination unit determines the transmission power of the radio signal transmitted by the small base station based on the reception power of the radio signal from the general base station acquired by the reception power acquisition unit, when it is determined by the determination unit that the radio signal is transmitted from the general base station, and wherein the transmission power determination unit determines, as the transmission power of the radio signal transmitted by the small base station, a transmission power having the smaller value from the transmission power of the radio signal from the small base station determined based on the pathloss value and the transmission power of the radio signal from the small base station determined based on the reception power of the radio signal from the general base station.