A workpiece marking device operating automatically includes a support member, a transmission member, a feeding mechanism, a discharging mechanism, a driving mechanism, a positioning tool, and a marking mechanism. The transmission member conveys a workpiece, the feeding mechanism includes a driving assembly coupled to the support member and a lifting member coupled to the driving assembly. The discharging mechanism is positioned on the support member and above the transmission member. The discharging mechanism includes a driving assembly coupled to the support member and a lifting member coupled to the driving assembly of the discharging mechanism to move workpieces away after marking.