Heterobicyclic derivatives of the formula: wherein R1 is aryl which may have suitable substituent(s), ar(lower)alkyl which may have suitable substituent(s), halo(lower)alkyl, protected carboxy(lower)alkyl, acyl(lower)alkyl, heterocyclic group or heterocyclic(lower)alkyl which may have suitable substituent(s), R2 is aryl which may have suitable substituent(s) or heterocyclic group, and R3 is hydrogen, lower alkoxy or arylthio, and a pharmaceutically acceptable salt thereof which are useful as a medicament.