A thermal-head driving apparatus drives a thermal head having a plurality of heating resistors separated in a plurality of groups and disposed in one line, each of the heating resistors capable of being energized by heating pulses the number of which is controlled in accordance with the required density of the corresponding picture element, the heating resistors of the each group being adapted to be sequentially driven. The apparatus comprises a first unit for generating signals representative of time intervals of the heating pulses, which time intervals is determined to keep a temperature of the heating resistors above a predetermined temperature during operation, and a second unit for controlling a time intervals of heating pulses applied to the heating resistors in accordance with the signals from the first unit.