Provided is an antitumor agnet useful for the prevention or treatment of digestive carcinoma, leukemia, hypophyseal tumor, lung small cell carcinoma, thyroid carcinoma and nerve astrocytoma.The antitumor agent comprises, as an active agent, a 1,5-benzodiazepine derivative represented by the following general formula (1) or a pharmacologically acceptable salt thereof:[Structure 1]wherein R1represents an C1-6allkyl group, R2represents a phenyl group or a cyclohexyl group, and Y represents a single bond or an C1-4alkylene group.本發明提供一種可治療或預防消化器官癌、白血病、腦下垂體腫瘤、肺小細胞性癌、甲狀腺癌及神經星狀細胞腫瘤之抗腫瘤劑。該抗腫瘤劑係以下列通式(1)之1,5-苯二氮平衍生物或其藥學上容許之鹽做為有效成分:(式中,R1表示C1-6烷基,R2表示苯基或環己基,Y表示單鍵或C1-4伸烷基)。
