Abstract: The present invention provides a process of preparing a compound of the formula [I]: wherein X is a group of the formula: —N? or —CH?; R1 is a hydrogen atom, a halogen atom, a lower alkyl group, a lower alkoxy group, a cyano group or an amino group optionally substituted by a lower alkyl group; Ring A is a nitrogen-containing heterocyclic group; Ring B is an optionally substituted benzene ring or an optionally substituted pyridine ring; and R3 is a hydrogen atom or a lower alkyl group, or a pharmaceutically acceptable salt thereof, which is useful as an inhibitor of activated blood coagulation factor X.