A method comprising: a first process of placing a laminated rotor core in a preheating device to preheat the laminated core; a second process of removing the preheated laminated core from the preheating device and disposing the laminated core between upper and lower dies of a resin sealing apparatus; a third process of pressing the laminated core by the upper and lower dies and liquefying resin material in resin reservoir pots by heating; and a fourth process of ejecting the liquefied resin material from the pots into the magnet insertion holes by plungers inserted and moving vertically in the pots and thermally curing the resin material. The method improves efficiency of resin sealing the permanent magnets in the laminated core.