PURPOSE: To prevent a furnace wall tube from wear and to improve the workability at the time of extracting a fluidized medium by making it possible to secure a proper fluidity of the fluidized medium without reducing a heat absorption area of the furnace wall tube in the furnace wall tube wear preventive device of a fluidized-bed boiler.

CONSTITUTION: Wear preventive plates 14 are welded to a furnace wall tube 12 at a certain inclination angle which is greater than the angle of repose of a fluidized medium 9 and in a zigzag shape. The interval between the furnace wall tube 12 and inside layer heat transfer tubes 13 is constituted to be narrower than the interval between the heat transfer tube groups 13. Consequently, the fluidized medium 9 flows while making contact with the inside layer heat transfer tubes 13 at the central part of the layer to transfer hart. Further, in the vicinity of the furnace wall tube 12, the flow speed of the fluidized medium is suppressed by the wear preventive plate 14, and flows in a zigzag manner along the angle of inclination of the plate 14 to transfer heat to the furnace wall tube 12. On the other hand, the operation of the fluidized-bed boiler is stopped, and when the fluidized medium 9 is extracted, the fluidized-bed medium 9 falls down along the wear preventive plates 14 inclined more than the angle of repose as if it wear rolling thereon.