A fluidized bed apparatus includes a fluidizing container, a porous plate, a lower spray nozzle, a bag filter, an upper spray nozzle, a backwash nozzle, and a backwash nozzle elevator. The fluidizing container is formed in an inverted truncated conical cylindrical shape. The porous plate is provided so as to block a lower opening of the fluidizing container. The lower spray nozzle jets out air into the fluidizing container via the porous plate. The bag filter is provided at an upper opening of the fluidizing container. The upper spray nozzle sprays spray liquid downward. The backwash nozzle sweeps away powder particulates adhered to the bag filter by jetting out air from the outside of the bag filter toward the inside and is moved up and down by the backwash nozzle elevator. The fluidizing container may be vibrated by a vibrator.