The present invention relates to a novel antiplatelet agent and a novel compound which is an active ingredient for the agent. The present invention provides the antiplatelet agent comprising a compound represented by the formula I: wherein, X is N, or CR 1d , X b1 -X b5 are the same or different, and are nitrogen or carbon, R 1a -R 1d are the same or different, and are hydrogen, an optionally substituted aklyl, an optionally substituted alkoxy, an optionally substituted akylthio, an alkenyl, a cycloalkyl, a halogen, cyano, or hydroxyl or optionally substituted by 1 or 2 alkylamino, R 2 is an optionally substituted aryl or an optionally substituted heteroaryl, R 3 is an optionally substituted aryl or an optionally substituted heteroaryl, or pharmaceutically acceptable salt thereof as an active ingredient.
