[Problem] To realize a technique whereby the proliferation rate of tumor cells can be more decreased by administering a mixture comprising less expensive moromi (sake mash) vinegar. [Solution] The proliferation rate of tumor cells is decreased by using a material comprising a mixture of marine alga-derived fucoidan and moromi vinegar. In particular, by using a mixture of acetyl fucoidan separated from Cladosiphon okamuranus Tokida with moromi vinegar, the less expensive moromi vinegar can substitute for the acetyl fucoidan and thus an effect of reducing the amount of the expensive acetyl fucoidan to be used can be achieved. The moromi vinegar as described above is used in an amount of 3-95%. The fucoidan as described above is derived from a marine alga such as Nemacystus decipiens, Undaria pinnatifida, Undaria pinnatifida sporophyll, Laminariaceae algae, Sargassum fusiforme, Sargassum horneri (Turner) C. Agardh or a marine alga belonging to the family Sargassaceae.