A handpiece which can perform at least one of incision, ablation, and hemostasis of biological tissue using an acting member is configured to allow hemostasis through irradiation with low-temperature plasma and suppress heating and energization of the biological tissue at the time of hemostasis through irradiation with low-temperature plasma.A plasma irradiation device (20, 220, 420, 520, 620) has a gas flow channel (22, 222, 522) and an electric field generation section (30, 230, 530) and is provided in a handpiece. The gas flow channel (22, 222, 522) is a flow channel for supplying a gas from the outside of the handpiece to a distal end portion of the acting member. The electric field generation section (30, 230, 530) has a first electrode portion, a second electrode portion, and a dielectric member and is disposed in the gas flow channel (22, 222, 522). The electric field generation section (30, 230, 530) generates an electric field in a space within the gas flow channel (22, 222, 522) by using a potential difference between the first electrode portion and the second electrode portion, thereby producing low-temperature plasma discharge.
