A method for manufacturing a core (S1) includes: a coating step (S20) of adding an organic binder to a large particle group composed of silica-containing large particles, and coating surfaces of the large particles with the organic binder; a mixing step (S30) of mixing, after the coating step (S20), the large particle group and a small particle group composed of silica-containing small particles having a smaller particle size than the large particles; a laminate shaping step (S40) of forming, after the mixing step (S30), a molding in which a mixture of the large and small particle groups is used; and a sintering step (S60) of sintering the molding after the laminate shaping step (S40).