PURPOSE: To paint a long-sized object such as a pipe uniformly over the entire surface at one time by forming a fluidized dipping vessel into a tapered shape which is increasingly finer toward the lower part, charging a powder paint having different grain sizes therein and moving upward and downward the long- sized object to be painted.

CONSTITUTION: A fluidized dipping vessel 12 for a powder fluidized bed coating process is formed into a vertical tapered shape which is increasingly finer toward the lower part. A powder paint 9 consisting of several kinds of plastics, etc. having different grain sizes is charged into the vessel 12 and compressed air is fed thereto through a perforated plate 14 to suspend the paint 9. The object 1 such as the long-sized pipe is held vertically in this state and is moved upward or downward so that the entire surface of the object 1 is painted at one time. The grain sizes of the paint 9 are coarse at the lower part and fine at the upper part in the vessel 12. Thus the coarse powder paint 17 sticks on the bottom end 20 of the object 1 and the fine paint 18 sticks on the top end 19 whereby the uniform painting is accomplished irrespective of the difference in the dipping time between the top end 20 the bottom end 19.