A power amplifier includes a power splitter that splits a first signal into a second signal and a third signal delayed from the second signal by about 90°, a first amplifier that outputs a fourth signal by amplifying the second signal when a power level of the first signal equals/exceeds a first level, a second amplifier that outputs a fifth signal by amplifying the third signal when the power level of the first signal equals/exceeds a second level higher than the first level, a first phase shifter that receives the fourth signal and outputs a sixth signal delayed from the fourth signal by about 45°, a second phase shifter that receives the fifth signal and outputs a seventh signal advanced from the fifth signal by about 45°, and a combining unit that outputs an amplified signal of the first signal by combining the sixth and seventh signals.