A reaction method for reacting a reaction object with a liquid containing the reaction object being in contact with a granular porous body, wherein the reaction object is a low-molecular-weight compound having a molecular weight of 2000 or less, the method includes a column flow method in which the liquid is caused to pass through a column filled with the granular porous body, so that the liquid is diffused in the granular porous body, or a shaking method in which the granular porous body is dispersively added in the liquid, and the liquid and the granular porous body are shaken to diffuse the liquid in the granular porous body, the granular porous body includes a skeleton body including an inorganic compound having a three-dimensional continuous network structure, and has a two-step hierarchical porous structure including through-holes formed in voids in the skeleton body, and pores extending from a surface to an inside of the skeleton body and dispersively formed on the surface, a most frequent pore diameter in a pore diameter distribution of the pores is within a range of 5 nm or more and 50 nm or less, a most frequent pore diameter in a pore diameter distribution of the through-holes is equal to or more than 5 times of the most frequent pore diameter of the pores, and within a range of 0.1 μm or more and 50 μm or less, a particle diameter of the granular porous body is equal to or more than 2 times of the most frequent pore diameter of the through-holes, and within a range of 20 μm or more and not more than an upper limit D (mm) defined depending on a contact time T (seconds) between the liquid and the granular porous body, the upper limit D is given by: D = 0.556 × LN T + 0.166 where the function LN is a natural logarithm in a case of the column flow method in a non-circulation type in which the liquid is caused to continuously pass through the column while a concentration of the reaction object in the liquid is kept constant; or D = 0.0315 × T + 0.470 in a case of the column flow method in a circulation type, in which the liquid after the reaction is returned to the column, and continuously circulated, and the shaking method, and the contact time T (seconds) is given by: a value obtained by dividing a volume (m 3) of the granular porous body by a flow rate (m 3 /second) of the liquid in the case of the column flow method in a non-circulation type; a value obtained by multiplying a fluid flow time (seconds) of the liquid by a volume ratio obtained by dividing the volume of the granular porous body by a volume of the liquid in the case of the column flow method in a circulation type; or a value obtained by multiplying the volume ratio by an elapsed time (seconds) after addition of the granular porous body in the liquid in the case of the shaking method, and the inorganic compound is an inorganic oxide containing a typical metal element or a transition metal element, or an inorganic oxide including a composite containing an alkali metal element, an alkaline earth metal element, or a lanthanum-based element. a value obtained by dividing a volume (m 3) of the granular porous body by a flow rate (m 3 /second) of the liquid in the case of the column flow method in a non-circulation type; a value obtained by multiplying a fluid flow time (seconds) of the liquid by a volume ratio obtained by dividing the volume of the granular porous body by a volume of the liquid in the case of the column flow method in a circulation type; or a value obtained by multiplying the volume ratio by an elapsed time (seconds) after addition of the granular porous body in the liquid in the case of the shaking method, and the inorganic compound is an inorganic oxide containing a typical metal element or a transition metal element, or an inorganic oxide including a composite containing an alkali metal element, an alkaline earth metal element, or a lanthanum-based element.