#$%^&*AU2016204054A120160707.pdf#####ABSTRACT An agent when used for potentiating antitumor effect of another anititumor agent, comprising 4-(2-fluoro-4-(3-(2-phenylacetyl)thioureido)phenoxy)-7-methoxy-N-m ethylquinoline-6-carboxamide (compound (I) ) , or a salt thereof as an active ingredient, wherein the other antitumor agent is a member selected from the group consisting of an antitumor antibiotic substance, an alkylating agent, a platina preparation, a pyrimidine-based antimetabolite agent, apurine-based antimetabolite agent, a folic acid antimetabolite agent, a plant alkaloid-based antitumor agent, a low molecular weight molecule targeted drug and an antibody molecule targeted drug.