Ultrasonic probe and ultrasonic treatment instrument

An ultrasonic probe having a longitudinal axis, the ultrasonic probe comprising:

• a probe main portion extending along the longitudinal axis, and configured to transmit an ultrasonic vibration from a proximal direction toward a distal direction;
• a hook provided on a distal direction side with respect to the probe main portion, and curved relative to the probe main body in a first perpendicular direction, which is one of directions perpendicular to the longitudinal axis, the hook forming a part of a distal surface of the ultrasonic probe;
• a first base surface provided in a part of an outer surface portion directed in the first perpendicular direction, and serving as a base plane of the hook protruding toward the first perpendicular direction, the first base surface extending toward the proximal direction from a hook proximal end, which is a boundary position between a root of the hook and the base plane, the first base surface being away from the longitudinal axis toward the first perpendicular direction by a distance which is constant at a predetermined dimension over an entire length of the first base surface in a longitudinal direction along the longitudinal axis;
• a second base surface provided in a part of the outer surface portion directed in a second perpendicular direction opposite to the first perpendicular direction;
• and
• a protrusion continuous with the distal direction side of the second base surface, and protruding toward the second perpendicular direction with the second base surface being as a base plane, the protrusion extending toward both the proximal direction and the distal direction from a reference position located on a section, which passes through the hook proximal end of the hook and which is perpendicular to the longitudinal axis.