The present invention is directed to a method for producing a cyclic diamine compound (3) or a salt thereof through the following scheme: (wherein Ar represents a phenyl group, a pyridyl group, or a pyrimidinyl group, any of which may have a substituent； X represents NH, S, or O； ring A represents a benzene ring or a pyridine ring, which may have a substituent； 1 represents an integer of 1 or 2； m represents an integer of 1 or 2； and n represents an integer of 1 to 6). The method enables synthesis of a cyclic diamine compound (3) or a salt thereof, which serves as an ACAT inhibitor, in an industrially useful manner.
