The formation of cracks is suppressed in a drying process for a water-containing wet gel without modifying the gel and without using a reagent. A water-containing wet gel is dried by removing water and then removing the remaining solvent. For example, a wet-gel container storing water-containing wet gel, containing a wet gel and a solvent, is heated. The solvent is vaporized into an upper space of the wet-gel container. The solvent-containing gas diffuses into a dehydrating agent container, and water is removed by a dehydrating agent. This state is maintained for one to two days to remove almost all amount of water from the solvent. Thereafter, the dehydrating agent container is detached and the wet gel, from which water has been removed, is heated to almost completely remove the solvent, and further heated at a higher temperature to completely remove the solvent to obtain a crack-free dry gel.