A transmission power control system includes a control and a controlled station. In the control station, an SIR (Signal-to-interference Ratio) estimator calculates two different kinds of estimated SIRs having a long and a short mean processing time, respectively. A subtractor subtracts a target SIR from the estimated SIR with the long mean processing time while an error decider compares the resulting difference with a threshold to thereby output a result of decision. A comparison value updater updates, based on the result of decision, a comparison SIR held in a comparison value holder. Another subtractor subtracts the comparison SIR from the estimated SIR with the short mean processing time. A control information converter generates power control information in accordance with the output of the another subtractor. The controlled station selectively increases or decreases transmission power in accordance with the power control information received from the control station.