An epoxy compound of high-purity N,N,N′,N′-tetraglycidyl-3,4′-diaminodiphenyl ether is produced by: an addition reaction step of reacting 3,4′-diaminodiphenyl ether with epichlorohydrin in a polar protic solvent at 65 to 100° C. for 12 hours or longer to form N,N,N′,N′-tetrakis(3-chloro-2-hydroxypropyl)-3,4′-diaminodiphenyl ether; and a cyclization reaction step of reacting the N,N,N′,N′-tetrakis(3-chloro-2-hydroxypropyl)-3,4′-diaminodiphenyl ether with an alkali compound for dehydrochlorination.