every dot on the line 0 d in 7 0 is converted into a print signal d out 7 0 through the conversion table 12 that is the same signal as the input color density signal is outputted as the print signal as to every dot when the conversion operation finishes the print signals are converted through the tph i f 13 into energizing signals which drive the tph 14 to print the line 0 the above corresponds to s4 in fig5 a next in order to convert the line 1 which is an odd numbered line an evenline signal 34 l 34 is given to the conversion table 12 then in order to convert the dot 0 which is an even numbered dot an evendot signal 34 h 34 is given to the conversion table 12 in this state according to the truth table in fig2 a color density signal of the line 1 and the dot 0 is converted through the conversion table 12 into ooh which indicates blank data not to be printed then in order to convert the dot 1 which is an odd numbered dot an evendot signal 34 l 34 is given to the conversion table 12 in this state according to the truth table in fig2 a color density signal of the line 1 and the dot 1 d in 7 0 is converted into a print signal d out 7 0 through the conversion table 12 that is the same signal as the input color density signal.