An ultrasonic treatment apparatus includes an ultrasonic probe having an ultrasonic vibration generator for generating ultrasonic vibrations and a vibration transmission member for transmitting generated vibrations, and a sheath for covering at least an outer peripheral surface of the vibration transmission member of the ultrasonic probe, and a fluid supply unit, attached to an attaching portion of the sheath, for supplying a fluid into a path defined between the vibration transmission member and the sheath. A seal member for sealing the path is arranged nearer to the vibration generator than the attaching portion of the sheath.