An ultrasonic treatment device includes a sheath, a probe inserted through the sheath in a state that a probe distal surface is positioned to a distal direction side of a distal end of the sheath, a suction passage defining portion defining a suction passage along a longitudinal axis inside the probe, and a clearance defining portion defining a clearance between a sheath inner peripheral portion and a probe outer peripheral portion. The ultrasonic treatment device includes a suction port defining portion defining a suction port, the suction port communicating with the suction passage, in the probe outer peripheral portion in a state that a part of the suction port becomes a non-exposed portion whose outer peripheral direction side is covered with a sheath, and an opening defining portion defining an opening in a sheath outer peripheral portion, the opening communicating with the clearance.
