The present invention provides an antitumor agent comprising a staurosporin derivative or a pharmaceutically acceptable salt thereof, as an active ingredient, which is represented by the general formula (I): wherein R1 represents hydrogen, hydroxy or lower alkoxy, R2 and R3 are the same or different and represent hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted lower alkenyl, substituted or unsubstituted lower alkynyl, substituted or unsubstituted aryl, a substituted or unsubstituted heterocyclic group, halogen, nitro, formyl, etc., R4 represents hydrogen, etc., R5 represents NR11AR12A (wherein R11A and R12A represent hydrogen, substituted or unsubstituted lower alkyl, etc.), provided that R2 and R3 are not simultaneously hydrogen.