A treatment device includes: a treatment body which including a treatment portion a cover covering a back surface of a treatment portion and an adjuster disposed between the treatment portion and the cover, and configured to adjust to increase a distance between the treatment portion and the cover in accordance with a rise in temperature of the back surface of the treatment portion due to the application of the energy and to increase an air layer region between the treatment portion and the cover, and to decrease the distance between the treatment portion and the cover in accordance with a fall in temperature of the back surface and to decrease the air layer region.
