A treatment tool includes an end effector, an elongated tubular shaft part, a first deflection part having a proximal end connected to a distal end of the tubular shaft part, a second deflection part having a proximal end connected to a distal end of the first deflection part and having a distal end connected to a proximal end of the end effector, and an operation part configured to operate the end effector, in which, when the first deflection part is deflected with respect to an axis of the tubular shaft part, the second deflection part is deflected to an opposite side with respect to the axis and a distal end of the end effector moves on the axis.