A printer, comprising: a printer body including a supplying part configured for rotatably holding and supplying a printing medium (L) 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 (L); 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 (L) 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 (L) 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 (L); 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 (L) 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 (L); 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 (L) 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 (L) 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 (L); 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 . <EOS>