To realize a printer and an ink ribbon tension controller in which use efficiency of ink ribbon can be enhanced significantly.

Before printing is started, winding diameter of an ink ribbon 36 wound around a winding reel 35 is calculated by measuring rotational amount of the winding reel 35 and a feed reel 34 for an identical time and then rotational amount of the winding reel 35 is controlled based on the winding diameter such that tension of the ink ribbon 36 is kept in a specified state between the feed reel 34 and the winding reel 35. Since the ink ribbon 36 can be stretched with an optimal tension between the feed reel 34 and the winding reel 35, use efficiency of the ink ribbon 36 can be enhanced significantly.