This paper describes how, to design the conical horn in ultrasonic machining ; it is as follows :
(1) The length of conical horn is determined by using the design chart which is got by solving numerically the frequency equation of conical horn.
(2) In the case of conical horn having irregular sinking form, we can determine its length by this experimental results.
This way is useful in determining the last length of horn without experimental approximation or step by step method.