An object of the present invention is to provide an excellent agent for treating or preventing dementia, schizophrenia based on serotonin 5-HT 5A receptor modulating action. It was discovered that acylguanidine derivatives, in which the guanidine is bonded to one ring of a naphthalene via a carbonyl group and a cyclic group is bonded to the other ring thereof, exhibit potent the 5-HT 5A receptor modulating action and excellent pharmacological actions based on the action. The present invention is useful as an excellent agent for treating or preventing dementia, schizophrenia, bipolar disorder or attention deficit hyperactivity disorder.
