One object of the present invention is to provide a drug that is effective in treatments for and prevention of psychiatric disorders and in treatments for and prevention of neurological diseases, inhibiting a Group II metabotropic glutamate receptor.The object is solved by a 2-amino-bicyclo[3.1.0]hexane-2,6-dicarboxylic acid derivative represented by formula [I]: ##STR00001## (wherein R.sup.1 and R.sup.2 are the same or different, and each represents a hydrogen atom, C.sub.1-10alkyl group, etc; X represents a hydrogen atom or a fluorine atom; and Y represents an amino group, --SR.sup.3, --S(O).sub.nR.sup.7, --SCHR.sup.3R.sup.4, --S(O).sub.nCHR.sup.3R.sup.4, --NHCHR.sup.3R.sup.4, --N(CHR.sup.3R.sup.4)(CHR.sup.5R.sup.6), --NHCOR.sup.3 or --OCOR.sup.7), a pharmaceutically acceptable salt thereof, or a hydrate thereof and so on.