A radio-frequency (RF) power supply apparatus includes a first power supply, a second power supply, and a matching device connected to the first/second power supplies. The first power supply supplies first RF power to a load by outputting first RF voltage with a first fundamental frequency. The second power supply supplies second RF power to the load by outputting second RF voltage with a second fundamental frequency lower than the first fundamental frequency. The matching device generates a clock signal with a frequency higher than the first fundamental frequency and provides the clock signal to the first power supply. The first power supply generates, by using the clock signal, a waveform signal with the same cycle as the second RF voltage. The first power supply performs, by using the clock signal, frequency modulation control on the first RF voltage to be output from the first power supply.