Provided are a compound that is useful for the prevention of and/or as a treatment agent for a disease in which a group II mGlu receptor is involved； and a medical application of said compound. Provided is a compound repesented by formula (I) or a pharmaceutically acceptable salt thereof. (In the formula, R1 and R2 independently represent a hydrogen atom, a C1-4 alkyl or the like； ring A represents a C6-10 aromatic carbon ring group, a 4 to 10 membered saturated heterocyclic group or the like； R3 and R4 independently represent a hydrogen atom, a halogen atom, a C1-6 alkyl, a C1-4 alkoxy or the like； R5 and R6 independently represent a hydrogen atom, a C1-6 alkyl, a C1-6 alkoxy, an-NRaRb or the like； Ra and Rb independently represent a hydrogen atom, a C1-4 alkyl or the like； X represents a nitrogen atom or a -CRe-； and Re represents a hydrogen atom, a halogen atom, a C1-6 alkyl or the like).
