To synthesize a high purity latent catalyst expressed by a specified formula simply in a high yield by reacting a tertiary amine or a heterocyclic nitrogen-containing compound, a specified proton donor having at least two protons. which can be released outside the molecule, in a molecule and expressed by a specified formula, and boric acid in a solvent.

A latent catalyst expressed by formula II (wherein, X is a tertiary amine or a heterocyclic nitrogen-containing compound and is charged with a proton in the production process to form an onium cation HX+) dissolves an n-valent (n is an integer 2 or above) proton donor having at least two protons which can be released outside the molecule and expressed by formula I [wherein, Z1 is an organic group having substituents Y1, Y2 (Y1, Y2 are groups produced by a process in which mono-valent proton donatable substituents release protons) and can form chelate structure when the substituents Y1, Y2 are linked to a boron atom] and boric acid in a solvent in which a proton can be dissociated. A basic tertiary amine or a heterocyclic nitrogen-containing compound is reacted with it, and a product is obtained by neutralization.