[Summary] An external preparation formulation superior in the transdermal absorbability has been desired as a new administration route of aripiprazole. Transdermal absorption of aripiprazole has been enabled for the first time by appropriately combining aripiprazole and an organic acid (particularly fatty acid with low lipophilicity). That is, it has been found that more superior transdermal absorbability can be achieved by forming a salt by using a compound showing lipophilicity within the range of −1.5-2, such as fatty acid and the like. It has been further found that the transdermal absorbability is remarkable improved by appropriately selecting the solvent composition. As a result, since a new dosage form of aripiprazole other than oral preparation has been developed, a new transdermal absorption preparation of aripiprazole can be provided.