Thermal printer and drive control method of thermal head

A thermal printer comprising:

• a first thermal head which is so provided as to be brought into contact with one side of a paper and energizes a plurality of heater elements to print dot image data on the one side of the paper;
• a second thermal head which is so provided as to be brought into contact with the other side of the paper and energizes a plurality of heater elements to print dot image data on the other side of the paper;
• and
• a controller configured to control the energization cycles of the first and second thermal heads such that the energization time required for the first thermal head to print one dot-line data and energization time required for the second thermal head to print one dot-line data do not overlap each other,
• in the case where a character string of the same size and same line space is printed in dot image data on both sides of the thermal paper using the first and second thermal heads, the controller shifts the print start timing of the character string by the first thermal head and print start timing of the character string by the second thermal head from each other at least by the time required for forming the space between lines.