A method for producing an injection-molded body from a molding material containing a poly(3-hydroxybutyrate) resin includes: melting the molding material by heating the molding material to a temperature between a melting point peak temperature and a melting point peak end temperature in differential scanning calorimetry analysis of the molding material, wherein the difference between the melting point peak temperature and the melting point peak end temperature of the molding material is from 10 to 70° C.; injecting the molten molding material into a mold having a temperature of 30 to 80° C.; and cooling the molding material in the mold to crystallize and solidify the molding material.