Patent ID: 8401417

Claim:
A power supply device for passing a high-frequency current into an inductive load, comprising: a generating circuit configured to generate a DC voltage; a first switch element connected in series with the inductive load and configured to switch the DC voltage generated by said generating circuit; a driving controller adapted to turn said first switch element on and off; a variable-capacitance capacitor constructing a resonant circuit together with the inductive load; and a capacitance controller configured to control the capacitance of said variable-capacitance capacitor; wherein said capacitance controller controls the capacitance of said variable-capacitance capacitor so that the capacitance of the variable capacitance capacitor in a first period is larger than the capacitance of the variable capacitance capacitor after the first period, wherein the first period is a period from a timing when the first switch element is turned off until a predetermined time elapses.