In a printing apparatus, each application period is set as fixed period of time ranging from main heating start point to next main heating start point to form successive printed dots on a printing medium in sub-scanning direction of thermal head. A control unit executes application of sub pulse for auxiliary heating which, when applied independently, cannot realize color development on the printing medium, but, when applied for compensating main heating by main pulse as applied in next application period can realize color development thereon, relating to each of heater elements under constraint such that sub pulse is applied within current application period wherein color development cannot be realized on the printing medium, irrespective of whether next application period wherein main pulse for main heating is applied to realize color development on the printing medium starts immediately after current application period wherein color development is not realized.