An electrosurgical unit (also known as ESU machine, surgical diathermy machine, or cautery machine) is a medical device that uses high-frequency electrical current to cut tissue, coagulate blood vessels, and achieve hemostasis during surgical procedures. First introduced in the early 20th century, electrosurgical cautery has become an indispensable tool in modern operating theaters worldwide.

The electrosurgical generator converts standard electrical current into high-frequency alternating current (300 kHz to 3 MHz), which produces controlled thermal effects when applied to tissue. This enables surgeons to perform precise cutting with minimal blood loss, making HF electrosurgical generators essential equipment for hospitals, surgical centers, and operation theaters.