A print medium-conveying device comprising: a drum that conveys a print medium by winding a sheet-like print medium around an outer peripheral surface and performing rotation; a pressure roller that presses a front surface of the print medium wound around the outer peripheral surface of the drum and makes a back surface of the print medium contact the outer peripheral surface of the drum; back tension giving means having an adsorption holding surface to which the front surface of the print medium is adsorbed and held, for adsorbing and holding the front surface of the print medium to the adsorption holding surface in a position immediately before entry between the drum and the pressure roller, and giving back tension to the print medium; print medium information acquisition means for acquiring information of the print medium; and control means for controlling ON/OFF of adsorption of the print medium by the back tension giving means, based on the information of the print medium acquired by the print medium information acquisition means, wherein: the print medium is a paper and the information of the print medium acquired by the print medium information acquisition means is thickness of the print medium; and the control means compares the thickness of the print medium acquired by the print medium information acquisition means and a threshold set beforehand, turns on the adsorption of the print medium by the back tension giving means when the thickness of the print medium acquired by the print medium information acquisition means is less than the threshold, and turns off the adsorption of the print medium by the back tension giving means when the thickness is equal to or greater than the threshold. a drum that conveys a print medium by winding a sheet-like print medium around an outer peripheral surface and performing rotation; a pressure roller that presses a front surface of the print medium wound around the outer peripheral surface of the drum and makes a back surface of the print medium contact the outer peripheral surface of the drum; back tension giving means having an adsorption holding surface to which the front surface of the print medium is adsorbed and held, for adsorbing and holding the front surface of the print medium to the adsorption holding surface in a position immediately before entry between the drum and the pressure roller, and giving back tension to the print medium; print medium information acquisition means for acquiring information of the print medium; and control means for controlling ON/OFF of adsorption of the print medium by the back tension giving means, based on the information of the print medium acquired by the print medium information acquisition means, the print medium is a paper and the information of the print medium acquired by the print medium information acquisition means is thickness of the print medium; and the control means compares the thickness of the print medium acquired by the print medium information acquisition means and a threshold set beforehand, turns on the adsorption of the print medium by the back tension giving means when the thickness of the print medium acquired by the print medium information acquisition means is less than the threshold, and turns off the adsorption of the print medium by the back tension giving means when the thickness is equal to or greater than the threshold.