Method for manufacturing porous silica crystal

In a synthetic method for porous silica crystals through a hydrothermal reaction, a method for synthesizing porous silica crystals with a size of 0.5 mm or larger in high reproducibility and efficiency is provided using a method for manufacturing the porous silica crystals, wherein a high concentration area with silicon is formed as a partial area inside a hydrothermal synthesis vessel, and at least a part of a surface-smoothed bulk material is present in the high concentration area with silicon to perform the hydrothermal reaction, the bulk material comprising a compound containing both silicon and oxygen as a supply source for a part or a whole of the structure composition elements of the porous silica crystals.