An antimicrobial agent comprising, as an active component, compounds represented by the following formula (I): [wherein, R 1 and R 2 each independently represent H or an alkali metal atom.]; and a microbicidal agent comprising, as an active component, compounds represented by formula (I): [wherein, R 1 and R 2 each independently represent H or an alkali metal atom.], wherein they have high safety and little impact on the environment.