A safe and practically useful body fluid processor whereby blood taken out from a patient can be directly processed, characterized by having a favorable passage of the blood cell and showing an extremely low risk of the generation and leakage of microparticles. Namely, a body fluid processor enabling direct hemoperfusion wherein the ratio of sedimented particles to the volume of the space in which the particles for processing body fluid are to be packed is 100% or less and the space in which the particles for processing body fluid are to be packed in the body fluid processor is filled with the particles for processing body fluid and a filling liquid at a ratio of 95% or more but not more than 100%.