PURPOSE:To obtain a carbonyl compound, having fluorine atom at the alpha-position or an alpha,beta-unsaturated carbonyl compound, having fluorine atom at the alpha-position and useful as a medicine, agricultural chemical or intermediate therefor, by reacting an enol compound with an N-fluoropyridinium salt. CONSTITUTION:An enol compound expressed by formula I (M is H, alkyl, aryl, acyl, etc.; R is H, alkyl, aryl, alkoxy, etc.; R -Ru5 are H, alkyl, alkenyl, etc.; n is 0 or 1) is reacted with a compound expressed by formula II (R -R are H, alkyl, aryl, etc., or may have a cyclic structure by various combinations), preferably in a solvent, e.g. CH2Cl2 or THF, at -80-+100 deg.C to afford the aimed compound expressed by formula III having good selectivity.