Provided is an HPA apparatus for a TDD wireless communication system. In the HPA apparatus, a power amplifier amplifies the power of an input signal. A gate bias controller turns on/off a gate bias of the power amplifier in accordance with a TDD control signal. A constellation error optimizer circuit removes a current fluctuation and a power noise, which occur when the gate bias controller turns on/off the power amplifier in a TX mode, to stabilize a drain bias thereof.