[Problem]To provide a compound useful as medicine having PDE4B inhibitory activity, in particular, as an active ingredient of a composition for treating or preventing schizophrenia, Alzheimer's disease, dementia, depression and the like.[Measures for Solution]The present inventors examined compounds having PDE4B inhibitory activity and found that a tricyclic or tetracyclic imidazo[1,2-a]pyridine derivative or salts thereof had a superior PDE4B inhibitory activity, thereby completing the present invention. The imidazo[1,2-a]pyridine derivative can be used as an agent for treating or preventing schizophrenia, Alzheimer's disease, dementia, depression and the like.
