The purpose of the present invention is to provide a hypochlorous acid aqueous solution having excellent antimicrobial effect and safety. An antimicrobial agent is provided which is a hypochlorous acid aqueous solution with a pH of 3.0-6.7, wherein the effective chlorine concentration in the aqueous solution is 50-260 ppm. Further, a sterilization method is provided characterized by immersing the member to undergo sterilization treatment in the aforementioned antimicrobial agent for 0.5-10 minutes. The antimicrobial agent has a broad antimicrobial spectrum of noroviruses, Staphylococcus aureus and other bacteria, yeast belonging to Rhodotorula, and Cladosporium cladosporioides and other fungi.
