A treatment tool comprising: an outer tube formed in a cylindrical shape along a longitudinal axis; an introducing tool formed in a cylindrical shape and configured to be attached to an opening formed in an abdominal wall, the introducing tool configured to be inserted by the outer tube; a treatment insertion portion configured to be inserted into the outer tube along the longitudinal axis; a treatment portion which is disposed at a distal end portion of the treatment insertion portion, the treatment portion being configured to perform a treatment; a treatment assisting portion (35, 90, 95) which is disposed at the distal end portion of the outer tube, the treatment assisting portion (35, 90, 95) having an assisting portion configured to assist an operation of the treatment portion during the treatment, the assisting portion having a plurality of joints (37, 39) configured to connect end portions of a plurality of links (36, 38) such that the treatment assisting portion (35, 90, 95) can move between a first position near the treatment portion and a second position away from the first position in a direction which intersects the longitudinal axis to be spaced apart from the treatment portion; a driving portion configured to move the assisting portion of the treatment assisting portion (35, 90, 95); an operating portion which is disposed at a proximal end portion of the outer tube; and a control portion (75, 85) configured to control the driving portion, characterized in that the treatment tool further includes an operation detection portion disposed at the introducing tool, the operation detection portion being configured to determine a movement amount of the assisting portion with respect to the introducing tool and an orientation of the assisting portion corresponding to an orientation of the introducing tool, and the control portion (75, 85) is configured to control the driving portion to move the assisting portion with respect to the treatment insertion portion by the plurality of links (36, 38) based on results determined by the operation detection portion. an outer tube formed in a cylindrical shape along a longitudinal axis; an introducing tool formed in a cylindrical shape and configured to be attached to an opening formed in an abdominal wall, the introducing tool configured to be inserted by the outer tube; a treatment insertion portion configured to be inserted into the outer tube along the longitudinal axis; a treatment portion which is disposed at a distal end portion of the treatment insertion portion, the treatment portion being configured to perform a treatment; a treatment assisting portion (35, 90, 95) which is disposed at the distal end portion of the outer tube, the treatment assisting portion (35, 90, 95) having an assisting portion configured to assist an operation of the treatment portion during the treatment, the assisting portion having a plurality of joints (37, 39) configured to connect end portions of a plurality of links (36, 38) such that the treatment assisting portion (35, 90, 95) can move between a first position near the treatment portion and a second position away from the first position in a direction which intersects the longitudinal axis to be spaced apart from the treatment portion; a driving portion configured to move the assisting portion of the treatment assisting portion (35, 90, 95); an operating portion which is disposed at a proximal end portion of the outer tube; and a control portion (75, 85) configured to control the driving portion, characterized in that the treatment tool further includes an operation detection portion disposed at the introducing tool, the operation detection portion being configured to determine a movement amount of the assisting portion with respect to the introducing tool and an orientation of the assisting portion corresponding to an orientation of the introducing tool, and the control portion (75, 85) is configured to control the driving portion to move the assisting portion with respect to the treatment insertion portion by the plurality of links (36, 38) based on results determined by the operation detection portion.