A treatment device includes: an insertion portion inserted into a channel of an endoscope a treatment section configured to perform treatment according to power supplied from a power source a power reception electrode installed along an outer circumferential face of the insertion portion and configured to form a capacitor by capacitively coupling to a power transmission electrode that generates an electric field according to the power supplied from the power source on an outer circumferential face of the channel when the insertion portion is inserted into the channel and a position restriction section that restricts a position of the insertion portion in the channel in a radial direction such that a distance between a center axis of the channel and a center axis of the insertion portion is equal to or smaller than a predetermined value.
