An electrostatic precipitator that can prevent the corrosion of a discharge electrode even if a gas to be treated containing a corrosive mist is treated. In an electrostatic precipitator having a discharge electrode arranged along a flow path of the gas to be treated, a spray nozzle that can spray a water to the upstream side of the discharge electrode is mounted. A wet film is formed on the surface of the discharge electrode with the water sprayed from the spray nozzle. The sprayed water is desirably a water vapor or a water droplet having a particle diameter of less than 10 μm.