Disclosed is a drug delivery system for delivering a drug at a sustained constant rate for a long period, which can be transplanted into an affected part safely and in a simple manner and can deliver a drug to the affected part for a long period. Specifically disclosed is a sustained drug delivery system in which an implant is implanted into a body, wherein the implant is a PEG capsule comprising a box-shaped PEG and a porous PEG sheet.
