Abstract: A CNC milling machine comprises a main transmission shaft driven by a motor, an upright shaft provided with a transmission wheel set that is actuated by the main transmission shaft, an engagement device having a main shaft which is provided with a connection member which is in turn provided with an engagement wheel set engaged with the main transmission shaft, and a horizontal shaft provided with a gear set mounted thereon such that the gear set is engageable with the main shaft of the engagement device. The upright shaft is actuated to turn via the transmission wheel set so as to enable an upright milling cutter of the upright shaft to carry out the longitudinal cutting of a workpiece. The horizontal shaft is actuated to turn via the engagement wheel set so as to enable a horizontal milling cutter of the horizontal shaft to carry out the horizontal cutting of the workpiece without having to transfer the workpiece.