Provided is a novel method for treating a cancer using an FTD/TPI combination drug, which shows remarkably excellent antitumor effect and small adverse effects. An antitumor agent, in which a combination drug containing trifluridine and tipiracil hydrochloride at a molar ratio of 1 : 0.5 and an anti-VEGF antibody or anti-EGFR antibody are administered in combination.本發明提供一種顯示顯著優異之抗腫瘤效果且副作用較少之FTD‧TPI複合劑之新穎癌治療方法。本發明之抗腫瘤劑之特徵在於:併用投予以莫耳比1:0.5含有三氟尿苷及地匹福林鹽酸鹽之複合劑、與抗VEGF抗體或抗EGFR抗體。