The powder classifying device classifies powder having a particle size distribution and collects the classified powder. The device includes a disc-like cavity to which the powder is supplied and where the supplied powder is classified, a powder supply port for supplying the powder to the cavity, guide vanes arranged so as to extend from an outer periphery of the cavity in an inner direction at a predetermined angle, a discharge unit for air streams including fine particles discharged from the cavity, a collection unit for coarse particles discharged from the cavity and air nozzles arranged below the guide vanes on an outer peripheral wall of the cavity along a tangential direction of the outer peripheral wall and blow compressed air into an inside of the cavity.