Disclosed is a bicyclic ?-amino acid derivative having an excellent activity as an a2d ligand. Specifically disclosed is a compound represented by the following general formula (I). [chemical formula 1] (I) (In the formula, R1, R2, R2', R4, R5, R6, R7, R8 and R8' each represents a hydrogen atom or the like; and R3 represents a hydrogen atom, a halogen atom, a C1-C6 alkyl group or the like.)