Thermal printer having a platen release mechanism for separating a platen away from a printing head, an idle rotation of a platen bearing is prevented while keeping a preferable attaching/detaching operation property of the platen.
In a thermal printer provided with a bearing (22) for rotatably holding a platen shaft (20a), a platen frame (24) movable for holding this bearing (22), an engagement groove (30A) provided in a body frame (30) so that the bearing (22) is engaged therewith in a position where the platen (20) is brought into contact with a printing head and a lock arm (32) for retaining a part of the bearing (22) and locking the bearing (22) under the condition that the bearing (22) is engaged with the engagement groove (30A), the bearing (22) is formed into a rhombus or an ellipsoid and the engagement groove (30A) is formed into a shape corresponding to the bearing (22).