An object of the present invention is to provide an activated blood coagulation factor X (FXa) inhibitor that reduces the risk of bleeding caused by the treatment of thromboembolism. The present invention provides an oral anticoagulant agent comprising a compound represented by the following formula (1): or a pharmacologically acceptable salt thereof, or a hydrate thereof, as an active ingredient, wherein (A) a factor involved in the risk of bleeding caused by the anticoagulant agent is selected as a dose determinant (B) a reference value of the dose determinant is set (C) the dose determinant of a patient in need of administration is measured and (D) the dose of the anticoagulant agent is selected with the reference value as an index.
