A high-frequency treatment instrument (1) that is used by being supplied with high frequency current from a power supply includes: a treatment portion main body (8) that is used to treat biological tissue； a conductive portion (9) that is provided on a surface of the treatment portion main body that is in contact with the biological tissue such that it is not electrically connected to the treatment portion main body； and a power supply device that electrically connects together the conductive portion and the power supply such that a conductive external surface thereof is not exposed, and that is positioned such that it is not electrically connected to the treatment portion main body. According to this high-frequency treatment instrument, it is possible to prevent supplied high frequency current leaking from portions other than the treatment portion, and to perform treatment efficiently.
