The present invention is a method that enables continuous injection molding of a thermosetting resin composition and reuse of an unnecessary part produced during the molding. The method includes injecting a thermosetting resin composition into a mold while a curing reaction of the resin composition is incomplete. The thermosetting resin composition is then cooled in the mold until becoming semi-cured and removed as a semi-cured product from the mold. The semi-cured product is separated from the unnecessary part and separately heated to progress a thermosetting reaction of the thermosetting resin composition. The unnecessary part may be used as a reworked raw material by regrinding the unnecessary part and mixing it with a fresh thermosetting resin composition. Then, a resultant mixture is used to perform a new injection molding.