Provided is a blood processing apparatus that can easily escape toward the dialysate port outlet of the housing without impairing the original function as an obstructing member and without air remaining in the space of the housing 2. The obstruction member (11) having a substantially cylindrical shape is arranged at a position where the dialysate port inlet 7.1 and / or the dialysate port outlet 7.2 is formed as viewed in the longitudinal direction of the housing 2. The obstruction member 11 has an opening 11OP formed along at least one portion in the side S direction along the longitudinal L direction. The opening 11O has a proximal-side opening 11OPE having a narrower width and a distal-side opening 11ODE having a wider width. The distal opening 11ODE and / or the proximal opening 11OPE are formed so that rounded portions R are formed in both side S directions and the degree of opening gradually changes. [Selection] Figure 5本来の障害部材としての機能を損なうことなく、かつエアーがハウジング２の空間に滞留することなく速やかにハウジングの透析液ポート出口方向へ抜けやすい血液処理装置を提供する。 ハウジング２の長手方向に見て、透析液ポート入口７.１及び／又は透析液ポート出口７.２を形成した位置に、略円筒状の障害部材（１１）を配置しているもので、当該障害部材１１は、側部Ｓ方向の少なくとも一箇所に開口部１１ＯＰを長手Ｌ方向に沿うように形成している。そしてこの開口部１１Ｏは、より狭い幅の基端側開口部１１ＯＰＥと、より広い幅の末端側開口部１１ＯＤＥとを有する。この末端側開口部１１ＯＤＥ及び／又は基端側開口部１１ＯＰＥは、両側部Ｓ方向にアール部Ｒを形成し、この開口度が徐々に変化するように構成している。【選択図】図５
