Present invention is a stent apparatus wherein a stent covering member holds a stent, which scaffolds a blood vessel from the inside when implanted in the blood vessel, in contracted state. The stent is formed of a biodegradable polylactic acid (PLA) as a tubular shape, shape memorized to a size capable of, when implanted in a vessel, scaffolding the blood vessel from the inside. This stent is held by the stent covering member in contracted state and mounted on a balloon of a balloon. The covering member is formed of a biodegradable polymer having elasticity as a cylindrical shape having an inner diameter to keep the stent in contracted state and, when the stent is expanded to the shape memorized shape, plastically deformed to release the holding of the stent. The stent and the stent covering member disappear in a vessel after they are implanted in the vessel.