A treatment device (12; 12a; 12b; 12c) which applies energy to a living tissue, comprising: a holding section (26; 206) which is adapted to hold the living tissue, the holding section (26; 206) including: first and second holding portions (52, 54; 222, 224) which relatively move with respect to each other; at least one output portion (56, 58; 126; 136; 144; 166, 168; 194, 196; 254, 274; 286) configured to be disposed on at least one of the holding portions and to supply energy from an energy source, the output portion being configured to thermally denature the living tissue by the energy supplied from the energy source at a time when the living tissue is held between the first holding portion and the second holding portion; and a cooling section (98; 108; 146, 156; 162a, 162b, 164; 292, 296; 298a, 298b) which is adapted to inhibit the spread of heat from the denatured living tissue to a surrounding area thereof, characterized in that the cooling section (98; 108; 146, 156; 162a, 162b, 164; 292, 296; 298a, 298b) includes a conduit (98; 156; 292; 298) having a thermal conductivity and adapted to pass a fluid for cooling through the cooling section (98; 108; 146, 156; 162a, 162b, 164; 292, 296; 298a, 298b), the conduit being different from the output portion, and each of the first and second holding portions (52, 54; 222, 224) comprises an edge portion (82a, 82b) having a contact surface that is configured to come into contact with the living tissue, wherein an outer peripheral surface of the conduit is cooled, the conduit (98; 156; 292; 298) is disposed outside the edge portions (82a, 82b) of the first and second holding portions (52, 54; 222, 224) such that a part of an outer peripheral surface of the conduit (98; 156; 292; 298) along the axial direction of the first and second holding portions (52, 54; 222, 224) and a part of the contact surface of the edge portions (82a, 82b) are configured to come into contact with the living tissue at a time when the living tissue is held between the first holding portion and the second holding portion, and the conduit (52, 54; 222, 224) is configured to contact the living tissue to draw heat from the living tissue when the living tissue is held by the holding portions (52, 54; 222, 224). first and second holding portions (52, 54; 222, 224) which relatively move with respect to each other; at least one output portion (56, 58; 126; 136; 144; 166, 168; 194, 196; 254, 274; 286) configured to be disposed on at least one of the holding portions and to supply energy from an energy source, the output portion being configured to thermally denature the living tissue by the energy supplied from the energy source at a time when the living tissue is held between the first holding portion and the second holding portion; and a cooling section (98; 108; 146, 156; 162a, 162b, 164; 292, 296; 298a, 298b) which is adapted to inhibit the spread of heat from the denatured living tissue to a surrounding area thereof, characterized in that the cooling section (98; 108; 146, 156; 162a, 162b, 164; 292, 296; 298a, 298b) includes a conduit (98; 156; 292; 298) having a thermal conductivity and adapted to pass a fluid for cooling through the cooling section (98; 108; 146, 156; 162a, 162b, 164; 292, 296; 298a, 298b), the conduit being different from the output portion, and each of the first and second holding portions (52, 54; 222, 224) comprises an edge portion (82a, 82b) having a contact surface that is configured to come into contact with the living tissue, wherein an outer peripheral surface of the conduit is cooled, the conduit (98; 156; 292; 298) is disposed outside the edge portions (82a, 82b) of the first and second holding portions (52, 54; 222, 224) such that a part of an outer peripheral surface of the conduit (98; 156; 292; 298) along the axial direction of the first and second holding portions (52, 54; 222, 224) and a part of the contact surface of the edge portions (82a, 82b) are configured to come into contact with the living tissue at a time when the living tissue is held between the first holding portion and the second holding portion, and the conduit (52, 54; 222, 224) is configured to contact the living tissue to draw heat from the living tissue when the living tissue is held by the holding portions (52, 54; 222, 224).