A biological component separation device that separates a predetermined biological component from a biological fluid, the biological component separation device comprising: a device main body formed of a soft material in a sheet-like shape, wherein a first sheet and a second sheet are joined together in a state of being superimposed on one another in a thickness direction; a filter member configured to partition an internal space of a filter accommodating unit provided in the device main body into a first chamber and a second chamber, and to capture the predetermined biological component; wherein an introduction port member disposed in the device main body and configured to introduce the biological fluid; and a lead-out port member disposed in the device main body and configured to deliver out the biological fluid, wherein the device main body is provided with an introduction line interconnecting the first chamber and the introduction port member, and a lead-out line interconnecting the second chamber and the lead-out port member, and in a state in which the device main body is suspended, a filter accommodating unit inlet where the filter accommodating unit and the introduction line are connected is positioned lower than a filter accommodating unit outlet where the filter accommodating unit and the lead-out line are connected, wherein the introduction port member and the filter accommodating unit inlet are connected by the introduction line, and the lead-out port member and the filter accommodating unit outlet are connected by the lead-out line, and the filter accommodating unit inlet is positioned lower than the filter accommodating unit outlet, and the introduction port member is positioned higher than the lead-out port member. a device main body formed of a soft material in a sheet-like shape, wherein a first sheet and a second sheet are joined together in a state of being superimposed on one another in a thickness direction; a filter member configured to partition an internal space of a filter accommodating unit provided in the device main body into a first chamber and a second chamber, and to capture the predetermined biological component; wherein an introduction port member disposed in the device main body and configured to introduce the biological fluid; and a lead-out port member disposed in the device main body and configured to deliver out the biological fluid, wherein the device main body is provided with an introduction line interconnecting the first chamber and the introduction port member, and a lead-out line interconnecting the second chamber and the lead-out port member, and in a state in which the device main body is suspended, a filter accommodating unit inlet where the filter accommodating unit and the introduction line are connected is positioned lower than a filter accommodating unit outlet where the filter accommodating unit and the lead-out line are connected, wherein the introduction port member and the filter accommodating unit inlet are connected by the introduction line, and the lead-out port member and the filter accommodating unit outlet are connected by the lead-out line, and the filter accommodating unit inlet is positioned lower than the filter accommodating unit outlet, and the introduction port member is positioned higher than the lead-out port member.