Abstract: An automatic tool changer in a machining enter includes a reducer, a compound cam, a cylindrical cam, a four-bar mechanism, a toggle mechanism, and a tool cahnge device. The compound cam and the cylindrical cam are driven by a motor after speed reduction through a belt and gear train. The compound cam includes a roller gear cam and a face cam performs the tool change motions. During the tool change motions, the cylindrical cam drives the crank of the toggle mechanism to make the slider push the drawback which produces the pushing and pulling tool motions in the spindle head. By way of using this design, the tool change time is largely reduced, the tool change motions are more smooth, and the cost can be cheaper than the previous design.