A power supply device includes: an oscillation unit for outputting a high frequency signal; a modulation unit for outputting a pulsed high frequency signal; a level adjustment unit for adjusting and outputting a level of the pulsed high frequency signal; a power amplifier for amplifying a power outputted from the level adjustment unit; an output power detection unit for detecting an output power value from the power amplifier; and a control unit. The control unit corrects and outputs a level control signal for controlling the level of the pulsed high frequency signal based on a corresponding correction factor at each of elapsed times in an on state of the pulsed high frequency signal, and compares comparison values in a current pulse and a previous pulse to update the correction factor such that comparison result between the set power value and the output power value becomes smaller at each reflection coefficient.