Abstract: In this paper, speed changing system for Horizontal Milling Machine (low speed position) is designed. In machine tool applications, the variety of speed are very important because of the cutting conditions. Cutting conditions, specially cutting speed, and feed speed depend mainly on the machined material properties and the surface finish accuracy. The purpose of a gearbox system is to convert input speed and torque into a different output speed and torques. The transmission consists of a train of gears of different size contain in a case. This paper emphasizes on the design consideration of speed changing system of gearbox for horizontal milling machine which has three speed two steps gear ratio.