An ultrasonic surgical apparatus comprising: an ultrasonic vibrator configured to generate ultrasonic vibrations; an ultrasonic probe which has a distal end portion and a proximal end portion and which is connected to the ultrasonic vibrator and which is configured to transmit the ultrasonic vibrations generated in the ultrasonic vibrator from the proximal end portion to the distal end portion in a longitudinal axis direction of the ultrasonic probe; a sheath unit into which the ultrasonic probe is inserted; a water supply channel which is provided inside the sheath unit and between the ultrasonic probe and the sheath unit and provided along the longitudinal axis of the ultrasonic probe and through which a liquid flows; a distal end opening portion which is provided at a distal end portion of the sheath unit to allow the liquid which has flowed through the water supply channel to flow out; and a treatment portion which is provided at the distal end portion of the ultrasonic probe to protrude outward from the distal end opening portion, which is configured to transmit the ultrasonic vibrations transmitted by the ultrasonic probe to a treatment part, and which is configured to treat the treatment part with the ultrasonic vibrations, wherein the treatment portion includes a treatment region configured to treat the treatment part with the liquid which has flowed out from the distal end opening portion and with the ultrasonic vibrations while the treatment region is in abutment with the treatment part, characterized in that the treatment portion further includes a hydrophilic region which is formed by the application of a hydrophilic coat and which is provided in part of the circumferential surface of the treatment portion to be provided from a distal end portion of the treatment region to an end portion of the treatment portion located in the distal end opening portion in the longitudinal axis direction. an ultrasonic vibrator configured to generate ultrasonic vibrations; an ultrasonic probe which has a distal end portion and a proximal end portion and which is connected to the ultrasonic vibrator and which is configured to transmit the ultrasonic vibrations generated in the ultrasonic vibrator from the proximal end portion to the distal end portion in a longitudinal axis direction of the ultrasonic probe; a sheath unit into which the ultrasonic probe is inserted; a water supply channel which is provided inside the sheath unit and between the ultrasonic probe and the sheath unit and provided along the longitudinal axis of the ultrasonic probe and through which a liquid flows; a distal end opening portion which is provided at a distal end portion of the sheath unit to allow the liquid which has flowed through the water supply channel to flow out; and a treatment portion which is provided at the distal end portion of the ultrasonic probe to protrude outward from the distal end opening portion, which is configured to transmit the ultrasonic vibrations transmitted by the ultrasonic probe to a treatment part, and which is configured to treat the treatment part with the ultrasonic vibrations, wherein the treatment portion includes a treatment region configured to treat the treatment part with the liquid which has flowed out from the distal end opening portion and with the ultrasonic vibrations while the treatment region is in abutment with the treatment part, characterized in that the treatment portion further includes a hydrophilic region which is formed by the application of a hydrophilic coat and which is provided in part of the circumferential surface of the treatment portion to be provided from a distal end portion of the treatment region to an end portion of the treatment portion located in the distal end opening portion in the longitudinal axis direction.