An antibacterial agent is obtained by steps in which: by reacting inorganic particles with a compound having a polymerizable ethylenically unsaturated group, a polymerizable ethylenically unsaturated group is attached to the inorganic particles； by co-polymerizing monomers having a functional group capable of binding to an antibacterial compound and the inorganic particles having an attached polymerizable ethylenically unsaturated group, a polymer having functional groups capable of binding to an antibacterial compound is bonded to the inorganic particles； and subsequently, by reacting an antibacterial compound with the inorganic particles bonded to the polymer having functional groups capable of binding to the aforementioned antibacterial compound, the aforementioned polymer bonded to the inorganic particles is converted into an antibacterial polymer.
