A thermal printer comprises a base part, a holding member, a printing device and a platen roller. When an uneven pressing force is applied to the printing device by the recording paper sheet, the printing device is capable of swinging about the support pin serving as a fulcrum in order to even out the pressing force. The deformable mechanism is capable of being plastically deformed to keep the position of the printing device. An elastic element is disposed between the holding member and the base part, and due to the elastic element, both the printing device and the platen roller are in close contact with the recording paper sheet when the recording paper sheet is clamped between the printing device and the platen roller. The printing force of the printing device acting on the printing paper sheet can be distributed more even to achieve clearer printing.