To obtain an antimicrobial agent capable of being widely applied to food-packaging materials, medical hygienic materials, etc., by simultaneously using two kinds of highly safe specific substances which can orally be administered into human bodies, and to obtain an antimicrobial coating material using the same.

This antimicrobial agent is prepared by mixing a cyclodextrin compound with a white cedar essential oil in a ratio of (99-60%)/(1-40%). The particle distribution of the mixture of the cyclodextrin compound with the white cedar essential oil is 0.5-150μm, and the maximum of the distribution is 3-15μm. The mixture is further mixed with a binder resin and a solvent to give the antimicrobial coating agent. The binder resin is preferably shellac, zein, methyl cellulose, etc., and the solvent is preferably the mixture of ethyl alcohol with propylene glycol or the mixture further mixed with water. The antimicrobial agent comprises the white cedar essential oil included in the cyclodextrin compound, thereby is a sustained release preparation, and has an effect retaining the antimicrobial action of the white cedar essential oil for a long time.