PROBLEM TO BE SOLVED: To provide a device and method for: inhibiting the attachment and retention of granular powders onto a filter during operation of a fluidized bed device； reducing the number of times of knocking off the powders by shaking or back washing in a treatment process； simplifying a treatment operation and improving operation efficiency； and also improving the uniformity of quality such as component content or grain size distribution of the granular powder product.SOLUTION: The upper ends of filter elements 8a1 of bag filters 8a are each supported by a support ring 8c through the elastic bodies 8b. The upper end of each bag filter 8a is vertically displaced within the range of displacement of the elastic body 8b by pulsation of a gas pulsating wave introduced in a fluidized bed vessel 1 and accordingly, the bag filter 8a repeats a slack state and tension state periodically. By such a periodical repeating operation, the fine powders attached to the surface of the bag filter 8a are knocked off to be returned to a lower fluidized bed.
