Abstract: An automatic tool changer in a machining center includes a reducer, a compound cam, a cylindric cam, a four-bar mechanism, an elliptic trammel mechanism, and a tool changer device. The compound cam and the cylindric cam are driven by a motor after speed reduction through a belt and gear train. The compound cam which is composed of a roller gear cam and a face cam performs the tool change motions. During the tool change motions, the cylindric cam drives the follower which is fixed on the slider of the elliptic trammel mechanism to make the other slider push the pull bar 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 smoother, and the cost is less expensive than the previous designs.