Abstract: A plasma processing apparatus in which a radio-frequency power supply modulates radio-frequency power such that the level of the radio-frequency power in a first period is higher than the level of the radio-frequency power in a second period. The second period alternates with the first period. A bias power supply modulates bias energy such that the level of the bias energy in a third period is higher than the level of the bias energy in a fourth period. The fourth period alternates with the third period. The bias power supply adjusts the time difference between the start point of the first period and the start point of the third period which partially overlaps with the first period according to the power coupling efficiency of the radio-frequency power to the plasma, obtained from a power of a traveling wave and a power of a reflected wave.