PURPOSE: To bring the temp. of a printing plate to an optimum temp. within a short time, by a method wherein plural sensors are provided to a heating printing plate while the high voltage of a rapid heating heater is blocked when a temp. in the vicinity ?of a printing optimum temp. is detected by a first sensor and low voltage is applied while regulated by the detection of the change in the temp. of a second sensor.

CONSTITUTION: When a power source is turned ON at the begining time of printing, a transistor Tr-1 is turned ON and high voltage Vb is applied to a heater 2 to abruptly raise the temp. of a printing plate 1. When the temp. thereof reaches a temp. T-1 slightly lower than a printing optimum temp. T-2, close the transistor Tr-1 and to block the high voltage Vb while only low voltage Vt sent from a control circuit 8 is applied to the heater 2. Subsequently, the low voltage Vt is gradually lowered until the temp. of the printing plate 1 reaches the printing optimum temp. T-2 by the action of a second sensor 4 and, when the temp. thereof reaches to the printing optimum temp. T-2, the low voltage Vt is made constant to hold the temp. of the printing plate to the printing optimum temp. T-2. Thereafter, the second sensor detects the change in the temp. of the printing plate and the low voltage Vt is regulated by the control circuit 8.