PROBLEM TO BE SOLVED: To provide an antimicrobial agent containing 6-substituted nicotinic acid ester derivative as an essential component.SOLUTION: An essential component is represented by the following formula, where Rrepresents a Cto Calkyl group, a Cto Calkoxy group, a Cto Calkoxymethyl group or an amino group, Rrepresents a hydrogen atom, a Cto Calkyl group or an amino group, Rrepresents a Cto Calkyl group, a Cto Calkoxy group, a benzyloxy group or a formula, Rrepresents a hydrogen atom, a halogen atom, a Cto Calkyl group or a Cto Calkoxy group, however Rrepresents a hydrogen atom or a Cto Calkyl group, when Rrepresents a Cto Calkyl group.