The utility model discloses an automatic mark apparatus of printing machine, which comprises a transverse guide rail which is mounted on the printing roller holder of the printing machine; a transverse support and a transverse motor are mounted on the transverse guide rail; the transverse support is connected with the transverse motor by a first transmission device; one end of the transverse support is vertically mounted with a vertical guide rail; a vertical support and a vertical motor are mounted on the vertical guide rail; the vertical support is connected with the vertical motor by a second transmission device; a mark pen is mounted on the vertical support; the transverse motor and the vertical motor are connected with the printing machine controller by lead wires. The advantages of the utility model lies in: it can realize transverse and vertical movement, and realizes interval paper mark; it needs no manual operation, and the controller can marks the papers needing mark automatically according to a preset program; thereby achieves high automation degree and high printing efficiency.