A heat generating element is constructed of at least a substrate, an insulating film disposed on the substrate, a heat generating portion provided with a thin film resistor disposed on at least a part of the insulating film, and a protective film disposed on the above-described insulating film and the above-described heat generating portion, wherein the above-described substrate and the above-described heat generating portion are composed of the same member. Additionally, a medical therapeutic instrument includes a treatment portion provided with the above-described heat generating element to heat a living body tissue by using the heat generated from the heat generating element and treat the living-body tissue. The heat generating element is mounted on the above-described treatment portion in such a manner that an outer surface of the above-described substrate of the heat generating element serves as a treatment surface.