To provide a curing method, by which a crack and a warpage are prevented from developing at the end part of a hardened hydraulic extrusion- molded matter.

In a thermally curing method performed by stacking trays, on each of which a hydraulic extrusion-molded body is placed, the open part of the tray is sealed by a barrier material, the thermal conductivity of which is 0.04 kcal/m2.h.°C or higher so as to thermally cure the molded body under the condition that no air goes in and out within the tray.