A treatment device includes a probe having a treatment portion to treat a biological tissue by using the ultrasonic vibration generated in an ultrasonic transducer; an action portion being able to be close to and away from the treatment portion and including a pressing portion that presses the biological tissue to the treatment portion; and a vibration damping portion disposed in a part of the pressing portion in a state of facing the treatment portion, moving following the treatment portion to which the ultrasonic vibration is transmitted when abutting on the treatment portion in a state where the ultrasonic vibration is transmitted to the treatment portion, and prevented from being grinded by the treatment portion to which the ultrasonic vibration is transmitted.