The disclosed technology is directed to a probe unit of an ultrasonic treatment tool that comprises an ultrasonic probe having respective opposed distal and proximal end sides in a longitudinal direction and configured to transmit ultrasonic vibrations. A treatment portion is attached to the distal end side of the ultrasonic probe in the longitudinal direction. The treatment portion includes a cutting surface of a shape having directionality. A handle portion having a cutting portion identifier that is engaged with an outer circumference of the proximal end side of the ultrasonic probe. The cutting portion identifier is configured to indicate a position of a reference side representing a direction in which the cutting surface is oriented and/or included in the cutting surface.