A blood reservoir that stores venous blood and/or cardiotomy blood, the blood reservoir comprising a housing , a venous blood filter means including a venous blood filter member for removing bubbles from the venous blood, and a cardiotomy blood filter means including a first cardiotomy blood filter member that removes foreign matter and bubbles from cardiotomy blood, and a second cardiotomy blood filter member that is disposed outside the first cardiotomy blood filter member and that removes foreign matter and bubbles from cardiotomy blood that has passed through the first cardiotomy blood filter member , the housing including a blood inflow portion and a blood outflow portion, the venous blood filter means disposed in the housing , the cardiotomy blood filter means disposed in the housing, the blood reservoir further comprising a guide member , the guide member being disposed between the second cardiotomy blood filter member and the outflow portion configured to guide blood that has been filtered by the filter means toward the outflow portion , wherein the guide member is made of a foam material and is a plate shaped member, characterized in that the guide member is compressed with respect to thickness direction, and is disposed at an angle of inclination that corresponds to the density of the material, such that the guide member is made of a foam material that has (i) a density in the range from 0.02 g/cm 3 to 0.05 g/cm 3 , and the angle of inclination is at least 70 degrees and over, or (ii) a density in the range from 0.05 g/cm 3 to 0.20 g/cm 3 , and the angle of inclination is from 65 degrees to 70 degrees, or (iii) a density in the range from 0.20 g/cm 3 to 0.40 g/cm 3 , and the angle of inclination is less than 65 degrees. the housing including a blood inflow portion and a blood outflow portion, the venous blood filter means disposed in the housing , the cardiotomy blood filter means disposed in the housing, the blood reservoir further comprising a guide member , the guide member being disposed between the second cardiotomy blood filter member and the outflow portion configured to guide blood that has been filtered by the filter means toward the outflow portion , wherein the guide member is made of a foam material and is a plate shaped member, characterized in that the guide member is compressed with respect to thickness direction, and is disposed at an angle of inclination that corresponds to the density of the material, such that the guide member is made of a foam material that has (i) a density in the range from 0.02 g/cm 3 to 0.05 g/cm 3 , and the angle of inclination is at least 70 degrees and over, or (ii) a density in the range from 0.05 g/cm 3 to 0.20 g/cm 3 , and the angle of inclination is from 65 degrees to 70 degrees, or (iii) a density in the range from 0.20 g/cm 3 to 0.40 g/cm 3 , and the angle of inclination is less than 65 degrees. (i) a density in the range from 0.02 g/cm 3 to 0.05 g/cm 3 , and the angle of inclination is at least 70 degrees and over, or (ii) a density in the range from 0.05 g/cm 3 to 0.20 g/cm 3 , and the angle of inclination is from 65 degrees to 70 degrees, or (iii) a density in the range from 0.20 g/cm 3 to 0.40 g/cm 3 , and the angle of inclination is less than 65 degrees. <EOS>