Recently, the market of oversea imported furniture has grown rapidly and rubberwood products receive high evaluation in Japan. This paper, then, aims to clarify business diversification in a furniture company, and to identify position of the new-furniture-material rubberwood in Japanese domestic furniture market. N, the leading furniture company, and some companies in Okawa were chosen to interview for the paper. N has built up its own specialized system to sell imported furniture by setting up subsidiaries abroad which are joint-venture manufactures and representative offices or branches. Since the 1990 s, N has started diversifying materials by using rubberwood to make the produce. Rubberwood helped reduce producing cost of the company, as it was cheaper compared to other wood materials. It satisfied the consumers who favoured cheap products. N expanded its scale of production, accordingly. Similarly, in Okawa, one of the traditionally famous places of furniture producers in Japan, although some manufacturers has been running down and recently imported less rubberwood due to the appearance of the companies like N, other companies have followed the N company to set up operations overseas and diversified their furniture materials by using rubberwood. From these results, the paper suggests that since rubberwood use has increased recently, and it played a big role in the producing expansion of the furniture companies, the sustainable management of rubber plantation should be taken into account.