The spray drying process and the apparatus therefor, of the present invention use a spray drying chamber formed by a heat-resistant porous membrane. Said porous membrane enables rapid separation of a discharge gas and a produced powder and accordingly total recovery of the produced powder from the spray drying chamber. Therefore, there occurs no nonuniformity in product composition; cleaning and blowing-off of adhered fine powder can be conducted rapidly and easily even in frequent product changes inevitable with a less grade larger quantity production system; as a result, a fine powder of higher quality and higher purity can be produced.