The ceramic slurry is prepared by mixing a ceramic powder, a solvent, a dispersion medium, an isocyanate, a polyol, and a catalyst for accelerating a urethane reaction between the isocyanate and the polyol. A temperature-sensitive catalyst, which substantially exhibits a catalyst function only within a specific temperature range including an active temperature and higher than room temperature, is used as the catalyst. In a solidifying and drying step performed after a molding step of the slurry at room temperature, the solidification/drying temperature is set to be a high temperature within the range (within the specific temperature range) relatively close to the active temperature of the temperature-sensitive catalyst, and this temperature is maintained. Thus, the catalyst function can sufficiently be exhibited under high temperature.