The present invention provides a tri-substituted pyrimidine compound having an excellent PDE10 inhibitory activity. The present invention relates to a tri-substituted pyrimidine compound represented by the following formula [I0] or a pharmaceutically acceptable salt thereof, a method for preparing the same, and use of said compound for PDE10 inhibitor, and a pharmaceutical composition comprising said compounds as an active ingredient: wherein: either one of X1 and X2 is N, and the other of X1 and X2 is CH； A is *-CH&boxH；CH&mdash；, *-C(Alk)=CH&mdash；, *-CH2&mdash；CH2&mdash； or *-O&mdash；CH2&mdash； (* is a bond with R1)； Alk is a lower alkyl group； Ring B is an optionally substituted nitrogen-containing aliphatic heterocyclic group； R1 is an optionally substituted quinoxalinyl or an optionally substituted quinolyl； Y0 is mono- or di-substituted amino group, or a pharmaceutically acceptable salt thereof.
