fig7 shows another example of the thermal resistive thin film this thermal resistive thin film 18 39 is formed like a strip covering all of end portions 13 and 14a 39 of the electrodes 11 and 12 and that area of the substrate 10 which is between these end portions 13 and 14a 39 thereof in addition each of the selective electrodes 11 is located on a line extending to the center between the two adjacent leads 14 39 of the common electrode 12 as can be easily understood the thermal resistive thin film 18 39 in this case can be more efficiently formed as compared with those of the first embodiment however there is the possibility that the surface of the paper sheet on which letters are printed is made dirty by current leaked from one of the selective electrodes 11 to the other selective electrodes 11 or to those leads 14 39 of the common electrode 12 which do not correspond to this one selective electrode 11 in theory it is confirmed by the inventors however that no influence of dirt by the above mentioned reason is appeared in the surface of the paper sheet and extremely excellent printing quality was thus achieved even when letters were printed at a high resolution of about 16 dots mm other components of this embodiment shown in fig7 are same as.