An automatic extrusion device includes a main body, a driving unit, a first transmission unit, a second transmission unit and an extrusion unit. The second transmission unit has a clutch slip function for the automatic extrusion device to extrude the front of the pipe to be in the form of a bell for a fast connection of pipes. Through the slip function of the second transmission unit, it not only prevents the extrusion unit from over extrusion but also makes the front end of the pipe round so as to beautify the interface of the pipe.