Provided is a compound that is an NMDA receptor antagonist having a broader safety margin, and is useful as an agent for treating or preventing Alzheimer's disease, cerebrovascular dementia, Parkinson's disease, ischemic apoplexy, or pain.A novel compound or a salt thereof, which is characterized in that it has an amino group and R1 (lower alkyl, cycloalkyl, -lower alkylene-aryl, aryl which may be substituted, and the like) on carbon atoms of indane, cyclopenta[b]thiophene, cyclopenta[b]furan, cyclopenta[b]pyridine, or cyclopenta[c]pyridine ring, or 2,3-dihydrdo-1-benzofuran, 2,3-dihydrdo-1-benzothiophene, indoline ring, or the like, and has R2 and R3 (the same or different, each lower alkyl or aryl) on carbon atoms beside them, and an NMDA receptor antagonist comprising the same as an active component.