It is intended to provide a continuous drug delivery system targeting a tissue in the posterior segment of eye which needs no frequent administration and shows little tissue invasion. Namely, a drug delivery system whereby a drug is selectively transferred into the posterior segment of eye, thereby lessening effects of the drug transfer on the anterior segment of eye. By administering fine grainscontaining a drug under Tenon's capsule, a drug delivery system ensuring the selective transfer of the drug toward the posterior segment of eye and maintenance of an efficacious drug concentration canbe constructed.