HIGH FREQUENCY POWER SUPPLY DEVICE

PROBLEM TO BE SOLVED: To prevent a high frequency output variation caused by fluctuation generated in output control, when a variation of a low frequency is produced in the load of a high frequency power supply device for supplying high frequency power to a plasma load etc.SOLUTION: The high frequency power supply device includes: a power variation period detector 10 for detecting a power variation period from either traveling wave power detected at the output side of a high frequency power generator 4 or reflected wave power; according to the detected power variation period, control period set means 11 for setting an appropriate control period value to prevent the occurrence of fluctuation in an average output value of the high frequency power generator caused by a difference between the control period and the power variation period; and a timing controller 12 for controlling timing of the high frequency power detector to detect high frequency power so that the control period is set to be a period set by the control period set means, and timing to supply a control signal to the high frequency power generator.