To control temperature of a sample in plasma processing with high accuracy while securing an electrostatic chucking force 5 without breakdown of an electrostatic chucking film. When radio-frequency power is time modulated, a high-voltage side Vpp detector detects a first voltage value which is a peak-to-peak voltage value of a radio-frequency voltage applied to a sample stage in a first period of the time modulation having a 10 first amplitude. A low-voltage side Vpp detector detects a second voltage value which is a peak-to-peak voltage value of a radio-frequency voltage applied to the sample stage in a second period having a second amplitude smaller than the first amplitude. Then, an ESC power supply control unit controls output voltages from 15 ESC power supplies based on the first voltage value, the second voltage value and a duty ratio of the time modulation.