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 represented by formula (1) 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).
