There is provided a transmission power control method in which trackability of up-transmission power control is improved using up-transmission power instruction information from radio base stations having down-links of a predetermined quality or more, and a mobile communication system and a mobile station apparatus that use this method. Radio base stations 11, 12 transmit up-transmission power instruction information for instructing mobile station 13 to lower up-transmission power when a receiving level of the up-link is not lower than an up-target value. Also, when the receiving level is below the up-target value, radio base stations 11, 12 transmit up-transmission power instruction information for instructing that up-transmission power be raised. Mobile station 13 determines up-transmission power using only up link transmission power instruction information from radio base stations having down-links of a predetermined communication quality or more, from among up-transmission power instruction information received from the plurality of radio base stations 11, 12 connected through soft handover.