A treatment instrument comprising: a first clamping surface which is formed by a first separate body (72; 122) and a second separate body (74; 124); a second clamping surface which is opposed to the first clamping surface such that the second clamping surface is capable of relatively approaching, and moving away from, the first clamping surface, and which is configured to clamp a living body tissue with the first clamping surface when the first clamping surface relatively approaches the second clamping surface; a pressure application member which is provided on the second clamping surface, and which includes an abutment portion that extends in a linear shape and is configured to apply a pressure to the living body tissue in a line shape when the first and second clamping surfaces (56; 58) relatively approach each other; and a moving mechanism (120; 150) which includes an urging body (76; 106; 108; 128; 154) configured to urge the first separate body (72; 122) and the second separate body (74; 124) to approach, or abut on, each other, characterized in that the moving mechanism (120; 150) includes a support body (102; 104; 126; 132) which is provided between the first separate body (72; 122) and the second separate body (74; 124) and which is pushed by the abutment portion by the first and second clamping surfaces (56; 58) relatively approaching each other, and the support body (102; 104; 126; 132), when being pushed by the abutment portion, is configured to move the first separate body (72; 122) and the second separate body (74; 124) away from each other such that tensile forces are applied to the living body tissue clamped between the first clamping surface and the second clamping surface, in directions deviating away from a direction along a line formed on the living body tissue by the pressure application member. a first clamping surface which is formed by a first separate body (72; 122) and a second separate body (74; 124); a second clamping surface which is opposed to the first clamping surface such that the second clamping surface is capable of relatively approaching, and moving away from, the first clamping surface, and which is configured to clamp a living body tissue with the first clamping surface when the first clamping surface relatively approaches the second clamping surface; a pressure application member which is provided on the second clamping surface, and which includes an abutment portion that extends in a linear shape and is configured to apply a pressure to the living body tissue in a line shape when the first and second clamping surfaces (56; 58) relatively approach each other; and a moving mechanism (120; 150) which includes an urging body (76; 106; 108; 128; 154) configured to urge the first separate body (72; 122) and the second separate body (74; 124) to approach, or abut on, each other, characterized in that the moving mechanism (120; 150) includes a support body (102; 104; 126; 132) which is provided between the first separate body (72; 122) and the second separate body (74; 124) and which is pushed by the abutment portion by the first and second clamping surfaces (56; 58) relatively approaching each other, and the support body (102; 104; 126; 132), when being pushed by the abutment portion, is configured to move the first separate body (72; 122) and the second separate body (74; 124) away from each other such that tensile forces are applied to the living body tissue clamped between the first clamping surface and the second clamping surface, in directions deviating away from a direction along a line formed on the living body tissue by the pressure application member.