A printing unit comprising: a head unit including a thermal head on which a plurality of heating elements are arranged; a platen unit to be combined with the head unit so as to be separable from each other, the platen unit including a platen frame, a subframe (22, 101), and a platen roller configured to feed a recording sheet; the platen frame including: a pair of shaft support portions configured to individually support both end portions of the platen roller; and a coupling portion configured to bridge the pair of shaft support portions; and the subframe being configured to movably support the platen frame; the printing unit further comprising: engagement concave portions formed on the head unit, which are configured to individually receive both the end portions of the platen roller and to hold the platen frame in a mounting position; a releasing lever provided to the head unit, the releasing lever being configured to disengage the platen roller from the engagement concave portions by pressing a portion of the platen frame, which is located on a side of one of the pair of shaft support portions, in a direction of disengaging the platen roller from the engagement concave portions; an abutment portion provided to the head unit, which is configured to come into abutment against the coupling portion of the platen frame when the platen frame is located at a mounted position in which the platen unit is combined with the head unit; and a pressure-applying mechanism provided between the platen frame and the subframe, which is configured to apply a pressure to the platen frame toward the abutment portion; wherein the subframe supports the platen frame movably through an intermediation of the platen roller. a head unit including a thermal head on which a plurality of heating elements are arranged; a platen unit to be combined with the head unit so as to be separable from each other, the platen unit including a platen frame, a subframe (22, 101), and a platen roller configured to feed a recording sheet; the platen frame including: a pair of shaft support portions configured to individually support both end portions of the platen roller; and a coupling portion configured to bridge the pair of shaft support portions; and the subframe being configured to movably support the platen frame; the printing unit further comprising: engagement concave portions formed on the head unit, which are configured to individually receive both the end portions of the platen roller and to hold the platen frame in a mounting position; a releasing lever provided to the head unit, the releasing lever being configured to disengage the platen roller from the engagement concave portions by pressing a portion of the platen frame, which is located on a side of one of the pair of shaft support portions, in a direction of disengaging the platen roller from the engagement concave portions; an abutment portion provided to the head unit, which is configured to come into abutment against the coupling portion of the platen frame when the platen frame is located at a mounted position in which the platen unit is combined with the head unit; and a pressure-applying mechanism provided between the platen frame and the subframe, which is configured to apply a pressure to the platen frame toward the abutment portion; wherein the subframe supports the platen frame movably through an intermediation of the platen roller. engagement concave portions formed on the head unit, which are configured to individually receive both the end portions of the platen roller and to hold the platen frame in a mounting position; a releasing lever provided to the head unit, the releasing lever being configured to disengage the platen roller from the engagement concave portions by pressing a portion of the platen frame, which is located on a side of one of the pair of shaft support portions, in a direction of disengaging the platen roller from the engagement concave portions; an abutment portion provided to the head unit, which is configured to come into abutment against the coupling portion of the platen frame when the platen frame is located at a mounted position in which the platen unit is combined with the head unit; and a pressure-applying mechanism provided between the platen frame and the subframe, which is configured to apply a pressure to the platen frame toward the abutment portion; wherein the subframe supports the platen frame movably through an intermediation of the platen roller.