PROBLEM TO BE SOLVED: To obtain the subject antimicrobial compound by an economical method comprising reacting an acyl chloride compound with an amine compound, while reducing the number of necessary raw materials and decreasing the number of processes. SOLUTION: An acyl chloride compound of formula I (R3 , R4 , R5 are each independently a halogen, a 1-4C alkyl, amino, etc.) is reacted with an amine compound of formula II (A is a monovalent anion; R1 , R2 are each H, a 1-4C alkyl, etc.; X, Y, Z are each H, a halogen, cyano, etc.,) in the presence of an amine (e.g. triethylamine), and a chlorine atom is subsequently selectively removed from the obtained dichloroacetonyl benzamide with hydrogen in the presence of a Pd catalyst to obtain the acetonyl benzamide of formula III.