Disclosed is a transmission power control method for controlling a target SIR which is a target ratio of signal to interference upon comparing error rate and target error rate of receive data on a receiving side, and causing transmission power control to be performed on a transmitting side in such a manner that measured SIR will agree with the target SIR. The method includes previously measuring and storing a correspondence characteristic between error rate and SIR; finding, from the correspondence characteristic, a first SIR with respect to a target error rate and a second SIR with respect to a measured error rate; and updating the target SIR by increasing or decreasing the target SIR by the difference between the first SIR and the second SIR.