Abstract: A drug delivery device includes a cylindrical casing which has two openings on opposite sides, a lid which has an air inflow hole and is joined at one end of the cylindrical casing so as to close one of the openings. An internal space, in which an inflating agent and a drug are sealed while being separated from each other, is formed by at least the cylindrical casing and the lid, the internal space communicates with the air inflow hole and a delivery hole through which the drug is delivered, the inflating agent is formed of a material which is mainly composed of iron, iron oxide is produced by at least oxygen in the inflow air, which causes the inflating agent to be inflated, and as the inflating agent is inflated, the drug is delivered through the delivery hole.