A combination of a printer and a ribbon cassette (45) has a mechanism for preventing a portion of the inked ribbon extending between a supply core (51) and a take-up core - (62) of the ribbon cassette (45) from shifting in the direction perpendicular to the longitudinal direction of the inked ribbon with respect to a printing head (40). The mechanism is constituted by a substantially planar surface of the platen - (13), and the printing head (40) is urged against the planar surface of the platen through the inked ribbon portion and a sheet (32) to which solid ink in the area on the inked ribbon portion is transferred by the printing head (40). The width of that area on the inked ribbon portion in the widthwise direc- ion of the inked ribbon is at most equal to a half of the width of the inked ribbon. Alternatively, the mechanism (400) is constitued by a mechanism operative in response to the variation in diameter of the inked ribbon wound on the supply core (51) for applying a variable back tension in the reverse direction to the tension acting on the inked ribbon portion by the take-up core (62).