A tool for surgical operation using ultrasonic waves is provided. The tool includes a transducer generating ultrasonic waves, a cylindrical bar-shaped transmitting rod for transmitting the ultrasonic waves, an end effector for cutting a surgical site using the ultrasonic waves transmitted from the transmitting rod, extended from one end of the transmitting rod, in which a part of the circular cross-sectional area thereof is flatly formed from the point corresponding to a second vibration node so as to allow gain step to start at the second vibration node, a rod cover for encompassing the transmitting rod using, as connection points, a plurality of vibration nodes formed when ultrasonic waves are transmitted through the transmitting rod, and a jaw for holding the surgical site while engaged with the end effector, is combined to one end of the rod cover in a pivotable manner, and is positioned to face the end effector.
