PROBLEM TO BE SOLVED: To provide a separation membrane device capable of suppressing contact between an adsorbent and a liquid to be treated and efficiently removing a substance to be removed. A hollow fiber membrane and a casing that covers the hollow fiber membrane are provided, and an average pore diameter (Do) of an outer surface of the hollow fiber membrane and an average pore diameter (Di) of an inner surface thereof are Do>； A separation membrane device, which has an inner dense structure satisfying the relationship of Di, and further includes fine particles having an average particle diameter in the range of 0.01 μm to 10 μm in the pores on the outer surface. [Selection diagram] None【課題】 吸着剤と被処理液の接触を抑制し、かつ除去対象物質を効率的に除去することが可能である、分離膜デバイスを提供する。【解決手段】 中空糸膜と、前記中空糸膜を覆うケーシングとを備え、前記中空糸膜の外側表面の平均細孔径（Ｄｏ)と、内側表面の平均細孔径（Ｄｉ）とが、Ｄｏ＞Ｄｉの関係を満たす内側緻密構造を有するものであり、 さらに、外側表面の細孔に、平均粒径が０．０１μｍ～１０μｍの範囲内である粉粒体が含まれてなる、分離膜デバイス。【選択図】なし
