PLATELET AGGREGATION INHIBITOR

PROBLEM TO BE SOLVED: To provide a novel platelet aggregation inhibitor capable of relieving or preventing various symptoms caused by aggregation of platelets, particularly, a platelet aggregation inhibitor available more conveniently and capable of being mass-produced easily.SOLUTION: The platelet aggregation inhibitor includes at least one compound selected from the group consisting of compounds having oxygen-containing circular structures represented by formulas (1) to (3) as an active ingredient. There are further provided blood flow improving agents and antithrombotic agents each containing the platelet aggregation inhibitor as an active ingredient.