The present invention provides a method of treating thrombocytopenia, which comprises administering to a patient suffering from thrombocytopenia, an effective amount of an indolocarbazole derivative represented by formula (I):

wherein R¹ represents a hydrogen atom, a substituted or unsubstituted lower alkyl group, a substituted or unsubstituted aralkyl group or a tetrahydropyranyl group; R 2A and R 3A , which may be the same or different, each represent a hydrogen atom, a substituted or unsubstituted lower alkyl group, a lower alkenyl group, a substituted or unsubstituted aralkyl group or a monosaccharide residue where a hydroxyl group at the anomer position is removed; R 4A and R 5A , which may be the same or different, each represent a hydrogen atom, a formyl group, a hydroxyl group or a halogen atom; W A represents two hydrogen atoms or an oxygen atom; and X A represents a single bond or two hydrogen atoms, provided that when X A forms a single bond, then R¹, R 2A , R 3A , R 4A , R 5A , and W A do not simultaneously represent a hydrogen atom, or a pharmaceutically acceptable salt.