Abstract
This study developed Gear Automatic Design Program that users with the basic knowledge about mechanical engineering can easily model spur gears and helical gears. The Gear Automatic Design Program used Visual LISP which is an user program based on Auto CAD and made it model the gears with involute tooth by the exact mathematic definition. Also, to verify these, the reliability was secured by comparing it with a gear generated in commercial software. And we will develop nitrocarburising process and solve problems which had been caused of SCM440's dimensional changing.