PURPOSE: To provide an antimicrobial agent having a high antimicrobial activity, substantially not corroding metal equipment, apparatuses, etc., not causing the deterioration of the antimicrobial activity because of not forming an insoluble complex even when mixed with an anionic surfactant, and suitable as a disinfectant for medical treatments, an environmental disinfectant, an antimicrobial agent for fibers, etc.

CONSTITUTION: An antimicrobial agent contains one kind or more of compounds selected from quaternary ammonium salts of the formula (R1 is 8-22C alkyl or alkenyl; R2 is 1-22C alkyl or alkenyl; R3 is 1-5C alkyl; R4 is alkylene; Ar is substitutable aryl or heteroaryl; Xm- is alkyl phosphate ion, polyoxyalkylene alkyl ether phosphate ion; m is 1,2; n is 1-5). The antimicrobial agent has an excellent antimicrobial activity and further excellent corrosion-resistant property and compatibility with anionic surfactants.