To provide a mobile station and a transmission power control method in the mobile station, which are capable of improving the power saving characteristic associated with the transmission power control in the mobile station under a condition in which the transmit diversity is applied. The transmission power of feedback information (11: FBI) is controlled on the basis of control information (TPC) transmitted through a sub-information downlink channel (21) from a base station (210) as a main branch, only when it is determined by a communication method determining section 103 that a cosed loop transmit diversity can be applied (step S201: Yes), and when it is determined by a communication base station determining section 104 that sub-information downlink channels (21, 22) and sub-information uplink channels (11, 12) are connected to a plurality of base stations (step S202: Yes).