PURPOSE: To enhance the time efficiency of mold and at the same time improve its productivity by a method wherein the temperature rise of the mold is done by setting a rising temperature, which is higher than a molding temperature, during a period ranging from the starting point of temperature rise to a temperature changing point, which is set on the basis of temperature condition and time condition, and, after the arrival of the temperature changing point, by setting the molding temperature.

CONSTITUTION: Heating medium 11 in a medium tank 12 is quickly heated so as to realize rising temperature of Tu by energizingly controlling an electric heater 18 under the condition that the set point of the rising temperature Tu is given to a temperature controller 6 after a power switch 25 is turned on. And the temperature Tp of the heating medium 11 is detected with a thermocouple 18 and inputted through the temperature controller 16 in a comparator 24. The output of the comparator 24 inverts under the condition that Tu≤Tp and the time of a timer 27 is up after the lapse of the set time counting period tc so as to change-over a change-over switch 30 to a first temperature setter 21 side. As a result, be set point of molding temperature Tm at the first temperature setter 21 is given to the temperature controller 16 so as to control the temperature of the heating medium to be equal to the molding temperature Tm.