To easily change pattern contents of a transparent protection pattern while preventing a cycle time during printing from being increased.

An I/F 21 receives image data and partial protection pattern data transmitted from a PC 90. The received image data is stored in frame memories 22a, 22b, and 22c. The received partial protection pattern data is stored in a pattern data storage part 23. A frame protection data generation circuit 24 generates frame protection pattern data by connecting the partial protection pattern data with each other. A head control circuit 25 controls a thermal head 2 so that an image is formed onto printing paper on the basis of the stored image data, and then, controls the thermal head 2 so that the transparent protection pattern is formed onto the printing paper on the basis of the generated frame protection pattern data.