The present invention relates to an extracorporeal High Intensity Focused Ultrasound (HIFU) necrosis apparatus through the control of an electronic signal, including oscillation elements for generating ultrasonic beams, an ultrasonic oscillator array having the oscillation elements fixed on a plane and oriented toward a life, delay circuits respectively connected to the oscillation elements for delaying ultrasonic oscillation by a delay time, and control means for controlling the delay time so that the ultrasonic beams are focused, and a method of employing the same. According to the present invention, waved surfaces with a variety of directions and curvatures can be formed using several oscillation elements and several delay circuits disposed on a plane, and a focus can be formed at any desired place. Accordingly, there are advantages in that installation is convenient, and a tissue, such as tumor, which is a target tissue, can be necrotized without damage to normal tissues necrosis. Further, there is no damage to normal tissues other than a target tissue. Accordingly, there are advantages in that a recovery speed of a patient can quicken, a symptom after recovery can be mitigated, and so on.