PROBLEM TO BE SOLVED: To obtain a desired cleavage reaction product corresponding to the kind of a reactive compound by a slight change in reaction conditions by reacting (meth)acrylic epoxide with the reactive compound such as boron trifluoride etherate complex. SOLUTION: (A) A compound of the formula [X is O, S, etc. ; R is H or a 1-5C alkyl; R is a 2-20C alkyl(aryl) containing an oxirane group in a chain or a chain end, glycidyl, etc.] is reacted with (B) a reactive compound selected from an inorganic strong acid (B1 ), boron trifluoride etherate complex (B2 ), an acid salt in the presence of a corresponding acid (e.g. sodium acetate in the presence of acetic acid) (B3 ), a trialkyl or a trialkoxysilane halide) (e.g. trimethylchlorosilane) (B4 ) and a ketone in the presence of a cationic resin (acetone in the presence of a sulfonated resin) (B5 ). The cleavage product the component A is useful in the field of ink, adhesive, paint, coating film, resin, etc.