It is intended to provide a blood bag system comprising one or more of containers capable of holding a liquid, and a connecting tube connected liquid-tightly to the container, characterized in that at least one of the containers holds an inactivator that inactivates a pathogenic microorganism contained in blood and/or an anticoagulant and the inactivator contains as a main component a platinum compound capable of binding to nucleic acids of the microorganism or an aquo complex of the platinum compound. According to the present invention, an effect of inactivating pathogenic microorganisms is increased and an excellent sustained inactivation effect is provided. Furthermore, transfusion of inactivated blood after neutralization treatment enables supply of microbiologically and toxicologically safe blood preparations.