A melt of Nd-Fe-B alloy is injected in an inert gas atmosphere through a nozzle against a chill roll or a pair of chill rolls rotating relative to the nozzle for contacting the melt with the circumference of the chill roll or rolls, thereby quenching the melt. The chill roll has a low heat conductivity surface layer around a base or has a predetermined surface roughness on its circumference. The contact time of the melt with the chill roll can be increased by blowing an inert gas flow. Further the melt is quenched in an inert gas atmosphere of up to 1 Torr. A wind shield is disposed in proximity to the chill roll circumference for preventing a wind of the ambient gas induced by rotation of the chill roll from reaching a paddle of the melt. With these means, there is obtained a permanent magnet material having a grain diameter with a reduced variation.