PURPOSE: To obtain the control device of a printer which gives steady printing quality by flowing a current for a specified time in printing cycles and extending the periods of the printing cycles when the temperature of a heating means reached a specified value.

CONSTITUTION: If the periods of printing cycles become short and the temperature of a dummy resistor 13 passes a specified value, a thermal switch 14 opens its contact points, opens the gate of a NAND gate 8 and triggers a monomulti 6, a print starting signal is converted into a printing signal after a time t equal to the time constant of the monomulti 6 passed and a printing cycle is started. Therefore, a time to enter a printing cycle is delayed, and so the periods of printing cycles become longer. As a result, the cooling time of an electromagnet 9 does fluctuate and a flight time does not change either. By so doing, steady printing quality is obtained.