PURPOSE: To enhance the safety against the breakage of each of piercing insulators, by dividing pressure blocking and temp. blocking to provide piercing insulators in two stages.

CONSTITUTION: The piercing insulators for supplying a current to the high temp. and high pressure container 6 of the pressure container of an electric precipitator are provided in two stages through a heat-insulated insulator chamber 4 having pressure equal to that of the container 6. Before-and-behind pressure difference is eliminated by the first insulator 3 piercing between the container 6 and the insulator chamber 4 and only temp. difference is held while before-and-behind temp. difference is eliminated by the second insulator 2 piercing between the insulator 4 and the outside and only pressure difference is held. By this method, the isolation from atmospheric pressure is finally performed and the safety of the insulators 2, 3 is held.