Power supply device for high frequency treatment instrument, high frequency treatment system, and control method for high frequency treatment instrument

A power supply device for a high frequency treatment instrument which treats living tissue by supplying high frequency power to the living tissue using an electrode, the power supply device comprising:

• an output unit which supplies the high frequency power to the electrode;
• a distance information acquisition unit which acquires distance information for a distance between the living tissue and the electrode, wherein the distance information acquisition unit acquires the distance information based on an impedance measured based on output by the output unit;
• a determination unit which determines whether the distance information satisfies a first condition or not;
• and
• an output control unit which controls the output unit so that the output by the output unit is placed in a controlled state if the distance information satisfies the first condition and so that the output is set to a first output level higher than an output level in the controlled state if a second condition is satisfied after the output is placed in the controlled state.