A handpiece is a surgical treatment instrument to treat a living tissue using electric energy and includes a probe configured to extend in a longitudinal direction from a proximal end portion to a distal end portion, and enabled to apply the electric energy to the living tissue and a shaft rod member configured to be disposed inside the probe, a portion of the shaft rod member closest to the probe being located away from the probe by a distance at which a discharge occurs at a voltage lower than a voltage at which a spark discharge occurs between the probe and the shaft rod member and higher than a voltage at which an arc discharge occurs between the probe and the shaft rod member.
