PURPOSE: To achieve the sharp reduction of equipment, the reduction of pressure loss and the increase of washing effect, by a method wherein a washing liquid is injected toward the oblique direction from a washing pipe and a mist eliminator is washed while the washing pipe is rotated on its own axis by the repelling action of a jet stream.

CONSTITUTION: Two washing pipes 12 are filled with a washing liquid A supplied to a pivot part 11 from a water supply pipe 16 and said washing liquid A is injected from spray nozzles 15 by its pressure. Because this injection is performed toward the oblique direction with respect to the surface of a mist eliminator 9, it has a horizontally directing vector and a vertically directing vector. Among them, the jet stream of the horizontally directing vector imparts the driving force of its repelling action to the washing pipe 12. Two washing pipes 12 receive couple because the spray nozzles 15 attached to said pipes 12 are present at a symmetric position and start rotation themselves. This rotation is extremely smooth because vibration is suppressed by support rollers 13 provided to the leading ends of both pipes 12.