In a plasma processing apparatus, first to third RF power monitors 94, 94 and 98 are configured to monitor high frequency powers (progressive wave powers), which propagate on first to third high frequency power supply lines 88, 90 and 92 from first to third high frequency power supplies 36, 38 and 40 toward a load side, respectively, and high frequency powers (reflection wave powers), which propagate on the first high frequency power supply lines 88, 90 and 92 from the load side toward the first to third high frequency power supplies 36, 38 and 40, respectively, at the same time. A main controller 82 is configured to control the high frequency power supplies 36, 38 and 40 and matching devices 42, 44 and 46 based on monitoring information sent from RF power monitors 94, 96 and 98.