A printing device with duplex printing function, comprising: a print head; a paper roll for rolling a printing media; a first paper path having a first end and a second end, the first end being connected to the paper roll; a second paper path connected to the second end of the first paper path and to the print head, the second paper path being suitable for reversing a bottom surface of the printing media to face the print head when the printing media is fed to the print head via the first paper path and the second paper path; a third paper path also extending from the second end of the first paper path; a cutting mechanism disposed on the third paper path, the cutting mechanism being for cutting the printing media into a printing sheet when the printing media is fed into the third paper path via the first paper path; and a fourth paper path connecting the third paper path and the second paper path, such that the printing sheet is fed from the third paper path into the second paper path via the fourth paper path, so as to be fed to the print head with a top surface of the printing sheet facing the print head; a first guiding gate mechanism disposed on the second end of the first paper path and for selectively communicating the first paper path with the second paper path or with the third paper path; and a second guiding gate mechanism disposed on a conjunction where the third paper path is connected to the fourth paper path and for selectively communicating the third paper path with the fourth paper path; wherein the first guiding gate mechanism is separate from the second guiding gate mechanism, and the cutting mechanism is positioned between the first guiding gate mechanism and the second guiding gate mechanism. a print head; a paper roll for rolling a printing media; a first paper path having a first end and a second end, the first end being connected to the paper roll; a second paper path connected to the second end of the first paper path and to the print head, the second paper path being suitable for reversing a bottom surface of the printing media to face the print head when the printing media is fed to the print head via the first paper path and the second paper path; a third paper path also extending from the second end of the first paper path; a cutting mechanism disposed on the third paper path, the cutting mechanism being for cutting the printing media into a printing sheet when the printing media is fed into the third paper path via the first paper path; and a fourth paper path connecting the third paper path and the second paper path, such that the printing sheet is fed from the third paper path into the second paper path via the fourth paper path, so as to be fed to the print head with a top surface of the printing sheet facing the print head; a first guiding gate mechanism disposed on the second end of the first paper path and for selectively communicating the first paper path with the second paper path or with the third paper path; and a second guiding gate mechanism disposed on a conjunction where the third paper path is connected to the fourth paper path and for selectively communicating the third paper path with the fourth paper path; wherein the first guiding gate mechanism is separate from the second guiding gate mechanism, and the cutting mechanism is positioned between the first guiding gate mechanism and the second guiding gate mechanism.