A compound represented by the formula (I): or a pharmaceutically acceptable salt thereof, wherein: R1 represents a branched lower alkyl group having from 3 to 9 carbon atoms or the like; R2 represents a 6-membered heteroaryl group having 1 or 2 nitrogen atoms or the like; R3 represents a hydrogen atom, an alkanoylamino group or the like; R4 represents a hydrogen atom, a lower alkyl group or the like; X1 represents an oxygen atom or a sulfur atom; X2 represents an oxygen atom or a single bond; and m indicates an integer of from 0 to 4. This compound has a metabotropic glutamate receptor 1 inhibitory effect, and therefore is useful for the treatment of a brain disorder such as convulsion, acute pain, inflammatory pain, chronic pain, cerebral infraction or transient cerebral ischemic attack, a mental dysfunction such as schizophrenia, and a disease such as anxiety and drug addition.