An apparatus for cutting pipes made of plastic material in automatic cutter machines, comprising: - a tool for cutting pipes made of plastic material, - a first arm, for supporting the cutting tool, movable between a non-operating configuration at which the tool is disengaged from the pipe and an operating configuration wherein the tool is designed to exert its cutting action on the pipe, - a second arm, for controlling the first arm, operatively connected to the first arm for moving the arm at least between its non-operating and operating configurations, the apparatus being characterised in that the second arm comprises a first electric actuator and a body for supporting the first electric actuator, the first electric actuator and the supporting body being connected either in a slidable fashion for modifying its reciprocal position between a close together position and a spaced apart position or connected like a compass to allow mutual rotation of the first electric actuator and the supporting body being pivoted to each other so as to extend rotating between themselves to modify the mutual distance of the relative ends between said close together position and said spaced apart position and in that it comprises: - a locking element for stably holding the first electric actuator and supporting body in one of either the close together position or spaced apart position, - disengaging means configured for releasing the locking element and allowing the first electric actuator and supporting body to reach the other between the close together position and spaced apart position. - a tool for cutting pipes made of plastic material, - a first arm, for supporting the cutting tool, movable between a non-operating configuration at which the tool is disengaged from the pipe and an operating configuration wherein the tool is designed to exert its cutting action on the pipe, - a second arm, for controlling the first arm, operatively connected to the first arm for moving the arm at least between its non-operating and operating configurations, the apparatus being characterised in that the second arm comprises a first electric actuator and a body for supporting the first electric actuator, the first electric actuator and the supporting body being connected either in a slidable fashion for modifying its reciprocal position between a close together position and a spaced apart position or connected like a compass to allow mutual rotation of the first electric actuator and the supporting body being pivoted to each other so as to extend rotating between themselves to modify the mutual distance of the relative ends between said close together position and said spaced apart position and in that it comprises: - a locking element for stably holding the first electric actuator and supporting body in one of either the close together position or spaced apart position, - disengaging means configured for releasing the locking element and allowing the first electric actuator and supporting body to reach the other between the close together position and spaced apart position. - a locking element for stably holding the first electric actuator and supporting body in one of either the close together position or spaced apart position, - disengaging means configured for releasing the locking element and allowing the first electric actuator and supporting body to reach the other between the close together position and spaced apart position.