PURPOSE: To reduce the facility of a high frequency generator by providing two high frequency power generators at a plurality of tire vulcanizing machines, and providing a time vulcanizing machine selecting and switching functions to become a maximum load at one generator.

CONSTITUTION: When a tire vulcanizing machine 5A starts vulcanizing, high frequency power is supplied from a large power high frequency generator 8 through a controller 6A for one min. In the meantime, the other vulcanizing machines are so limited as not to execute a vulcanization starting step. High frequency power is supplied from a power generator 9 to the other machines through controllers 7B-L. If the machine 5A finishes the starting step, the power from the generator 8 is switched to the machine 5B by a power switch 13B, and the machine 5B performs the starting step. The machine 5A is switched at power supply to the controller 7A to continue the vulcanizing step. Thus, a circuit for supplying large power is sequentially switched from A to L through the controller 6 to be operated.