A wireless base station unit (100) monitors total transmission power, which is a sum of transmission power to all of mobile station terminals (200-203) connected for communication. When the total transmission power exceeds a first threshold value, which is a criterion for judging whether to reduce the transmission power or not, an upper limit value of the transmission power to the mobile station terminal at the lowest priority level is reduced by a prescribed quantity. When the total transmission power exceeds a second threshold value, which is larger than the first threshold value, communication connection with the mobile station terminal at the lowest priority level is cut.