A printer, comprising: a printer body including a supplying part configured for rotatably holding and supplying a printing medium rolled into a rolled-shape; an opening and closing cover configured to open and close with respect to the printer body; a thermal head disposed on the printer body, the thermal head configured to print on the printing medium; a platen roller disposed on the opening and closing cover and detachable therefrom, the platen roller positioned at a location opposite to the thermal head and configured for feeding the printing medium in a closed state of the opening and closing cover; and a platen roller holding mechanism configured to hold the platen roller when the platen roller holding mechanism is attached to the opening and closing cover, the platen roller holding mechanism configured to release the platen roller when the platen roller holding mechanism is detached from the opening and closing cover, the opening and closing cover including a platen roller insertion opening configured to detachably insert a shaft of the platen roller thereinto, and the platen roller holding mechanism including a platen roller holder configured to be inserted into the platen roller insertion opening in order to close the platen roller insertion opening; characterized in that the platen roller holding mechanism includes a first roll supporter suitable for rotatably guiding the printing medium in the supplying part, the first roll supporter including a cross-sectional arc-shaped surface; the platen roller holding mechanism includes a second label guide upstream of the platen roller; the second label guide is configured to guide a rear surface side of the printing medium; the platen roller is rotatably attached to the platen roller holding mechanism; and the platen roller insertion opening and the platen roller holder form a long hole, and the platen roller is configured to freely move inside the long hole. a printer body including a supplying part configured for rotatably holding and supplying a printing medium rolled into a rolled-shape; an opening and closing cover configured to open and close with respect to the printer body; a thermal head disposed on the printer body, the thermal head configured to print on the printing medium; a platen roller disposed on the opening and closing cover and detachable therefrom, the platen roller positioned at a location opposite to the thermal head and configured for feeding the printing medium in a closed state of the opening and closing cover; and a platen roller holding mechanism configured to hold the platen roller when the platen roller holding mechanism is attached to the opening and closing cover, the platen roller holding mechanism configured to release the platen roller when the platen roller holding mechanism is detached from the opening and closing cover, the opening and closing cover including a platen roller insertion opening configured to detachably insert a shaft of the platen roller thereinto, and the platen roller holding mechanism including a platen roller holder configured to be inserted into the platen roller insertion opening in order to close the platen roller insertion opening; characterized in that the platen roller holding mechanism includes a first roll supporter suitable for rotatably guiding the printing medium in the supplying part, the first roll supporter including a cross-sectional arc-shaped surface; the platen roller holding mechanism includes a second label guide upstream of the platen roller; the second label guide is configured to guide a rear surface side of the printing medium; the platen roller is rotatably attached to the platen roller holding mechanism; and the platen roller insertion opening and the platen roller holder form a long hole, and the platen roller is configured to freely move inside the long hole.