Providing a novel cancer treatment method using an HSP90 inhibitor that exhibits a remarkably excellent antitumor effect and has few side effects. An anti-tumor agent comprising a combination of an azabicyclic compound represented by the following general formula (1) or a salt thereof and another anti-tumor agent.顕著に優れた抗腫瘍効果を示し、副作用の少ないHSP90阻害剤を用いた新規な癌治療方法の提供。 下記一般式(1)で表されるアザ二環式化合物又はその塩と他の抗腫瘍剤を併用投与することを特徴とする抗腫瘍剤。