A treatment device includes, a probe that conveys ultrasonic vibration and a high-frequency current; a treatment section that comprises a first treatment surface provided at a distal end of the probe for treating body tissue and a second treatment surface opposed to the first treatment surface, and treats the body tissue with the ultrasonic vibration and the high-frequency current conveyed to the first treatment surface and the second treatment surface via the probe; and an electrically-insulating coating portion that covers at least one of the first treatment surface and the second treatment surface.