A treatment apparatus to treat a body tissue includes a conductive heat transfer plate to transfer heat and power to the body tissue, an electrothermal conversion element provided on the heat transfer plate, the element including an electric resistance pattern that generates heat with a voltage applied, and a lead wire configured to supply an electric current to the heat transfer plate. Heat generation density by the electric resistance pattern in a first region of a pattern region where the electric resistance pattern of the electrothermal conversion element is formed, the first region including a region where a distance from the lead wire is smaller than a predetermined value, is higher than heat generation density by the electric resistance pattern in a second region including at least a part of the pattern region other than the first region.
