To provide a blood processing device, in which a blood processing member can secure an effective filtration area substantially two times greater than those of conventional ones and therefore it becomes possible to largely reduce the filtration time. [Solution] A first blood processing member 5U formed by stacking multiple non-woven fabrics each having a predetermined thickness and a second blood processing member 5D formed by stacking multiple non-woven fabrics each having a predetermined thickness are arranged in a first housing 2/U and a second housing 2/D, respectively. The first blood processing member 5U and the second blood processing member 5D are arranged in such a manner that inside filtration sections 5FI/U and 5FI/D face each other. A first blood chamber 2.1 is formed between the inside filtration sections 5FI/U and 5FI/D, and a second blood chamber 2.2 is formed between the inner periphery of the first housing 2/U and an outside filtration section 5FO/U of the first blood processing member 5/U and between the inner periphery of the second housing 2/D and an outside filtration section 5FO/D of the second blood processing member 5D. A blood inlet port 71 is formed so as to be communicated with the first blood chamber 2.1 (a blood inflow chamber 2IR), and a blood discharge port 7O is formed so as to be communicated with the second blood chamber 2.2 (a blood outflow chambers 20R/U and 20R/D).
