A treatment instrument includes a heat conductor which includes a treatment surface and an installation surface, a heat generator which generates heat, a substrate which includes a substrate front surface on which the heat generator is formed and a substrate side surface facing one side in a width direction, the substrate being attached to the installation surface, an adhesive layer which is provided between the installation surface of the heat conductor and the substrate, the adhesive layer being formed of a material having a thermal conductivity and being in close contact with the installation surface, and an insulating portion which is formed of a material having electrical insulation, the insulating portion being in close contact with the heat generator, the substrate front surface, and the substrate side surface.
