Disclosed is a treatment device for occluding a body lumen, including: a hollow shaft which can be inserted into the body lumen a flat portion forming section which has a pair of arms inserted in the shaft, the arms capable of being protruded from and retracted into a distal end opening of the shaft and expandable widthwise, and which deforms the body lumen into a form having a flat portion as the pair of arms is expanded within the body lumen and a heating section which is extendable and contractible in a width direction of the flat portion forming section, is extended as the pair of arms is expanded within the body lumen, and heats the flat portion.
