86 is connected to the thermal head 113 for supplying the printing data to the thermal head 113 the motor driver 88 drives a carriage motor 89 the flat motor 62 and the carrying motor 32 illustrated in fig4 and the carriage motor 89 rotates the screw shaft 65 as illustrated in fig7 to thereby move the carriage 64 the control portion 81 is mounted on the substrate 60 as illustrated in fig7 an operation of the thermal printer according to the first embodiment of the present invention will be described hereafter as illustrated in fig5 the printing sheet cartridge 52 is incorporated with the ink ribbon cartridge 10 by engaging the guide rails 53a and 53b of the printing sheet cartridge 52 with the grooves 54a and 54b of the ink ribbon cartridge 10 so as to constitute the expendable cartridge 59 then the upper unit 2 is opened as illustrated in fig3 and the expendable cartridge 59 is mounted on the mounting portion 16 of the lower unit 3 in the manner that the printing sheet cartridge 52 is disposed under the ink ribbon cartridge 10 at this time the side wall 17 is slightly bent in the direction of the arrow a as illustrated in broken lines to facilitate the mounting of the expendable cartridge 59 fig2 is the view showing a state where the expendable cartridge 59 is.