To provide a thermal printer apparatus and a printing method that can be adapted to different types of thermal paper having different thermal conductivity characteristics, a dot data memory 3 stores dot data for each line in synchronization with line sequential printing and delivers an energizing pulse selectively to a line thermal head 1 via a driving circuit 2. A multiplier 4 counts the number of dots to be printed for each line and multiplies a result of the counting by a heated thermal paper coefficient P1 corresponding to a thermal conductivity characteristic of a thermal paper 42. A heat accumulation counter 5 counts results of the multiplying in an accumulative manner. A multiplier 6 multiplies a count value in the heat accumulation counter 5 by a heat radiation coefficient and a heat radiation thermal paper coefficient P2 corresponding to the thermal conductivity characteristic of the thermal paper 42 repeatedly at a predetermined period, so as to correct and update the count value in the heat accumulation counter 5. An arithmetic unit 7 calculates an energizing pulse width based on the corrected and updated count value in the heat accumulation counter 5 in synchronization with line sequential printing, and controls the driving circuit 2 based on a result of the calculating.