An object is to provide a novel therapeutic drug for adult T-cell leukemia having an ATL cell specific antitumor effect. The therapeutic drug for adult T-cell leukemia according to the invention is characterized by containing a compound represented by the formula I or a prodrug thereof, wherein R1 is H, OH, an alkoxy group, an acyl group, or a thioacyl group, R2 is an acyl group, a thioacyl group, CONR7R8, or CSNR7R8 (R7 and R8 being each independently H, an alkyl group containing 1 to 3 carbon atoms, or a phenyl group), or R1 and R2 together may form a ring, X1 and X2 may be the same or different and are each —CR3R4—, —SiR3R4— or oxygen, and R3 and R4 may be the same or different and are each an alkyl group containing 1 to 6 carbon atoms.