A treatment energy application structure includes a flexible substrate having an electric resistance pattern and a lead wire connection portion. A heat transfer plate faces the flexible substrate and transfers heat to the body tissue. An insulating adhesive sheet is interposed between the flexible substrate and the heat transfer plate. The insulating adhesive sheet comprises a first area to cover an entire surface of the electric resistance pattern and the heat transfer plate and a second area protruding from the heat transfer plate to cover a part of the lead wire connection portion. The heat transfer plate has a chamfered corner facing the insulating adhesive sheet. An adhesive may adhere the second area to at least one of the heat transfer plate and the substrate. The insulating adhesive sheet may adhere the substrate to both the heat transfer plate and the bridge portion of a cover.
