If a top cover 5 has been opened, a link lever 34 is moved backward in conjunction with the motion of the top cover 5, so that a release lever 51 is rotated clockwise as seen from the left side about a level shaft 50. Also, a release gear 49 and a release shaft 48 are rotated about 180° counterclockwise as seen from the left side, via a lever gear 52. Accordingly, a head supporting member 37 is rotated downward, resisting an urging force of a pressing spring 36, so that a thermal head 32 is separated from a platen roller 35 and entry of a roll sheet 3A becomes possible through an insertion port 26.