An apparatus and method for flexibly changing a fixed target SIR, a fixed target SIR step size, and a time to perform a TX power control request, in order to prevent a receiver apparatus from performing an excessive TX power control request upon a sudden RX channel environment change in a mobile communication system. The apparatus includes a target Signal-to-Interference Ratio (SIR) determiner for flexibly changing a fixed target SIR upon a sudden target SIR re-decrease, after a previous increase, by decreasing a target SIR by a large step size at an initial stage of a sudden target SIR increase and decreasing the target SIR down-step size with an approach to a normal target SIR.