A blood filter device configured to filter a sample containing a liquid component and a plurality of solid components mixed with the liquid component, the blood filter device (100, 200) comprising: a container configured to store the sample therein; a tube configured to be inserted into the container; a filter part provided inside the tube, wherein, when the tube is inserted into the container, the filter part is configured to allow the stored sample to pass through the filter part so as to capture the plurality of solid components and to allow the liquid component to pass through the filter part; a capturing-retaining mechanism (104, 106, 204, 221) configured to prevent the plurality of captured solid components from being removed from the filter part when the sample passes through the filter part; and a cap provided at an opening end of the tube opposite to an opening end to which the filter part is joined and closing the opening end of the tube, the cap being configured to be removable from the opening end of the tube, wherein the cap is configured to hermetically seal the container to increase an inner pressure of the container when the tube is inserted into the container; wherein the container has an opening having the tube inserted therein, and wherein the capturing-retaining mechanism (104, 106, 204, 221) is structured such that: the capturing-retaining mechanism (104, 106, 204, 221) includes a first projection provided on an outer circumference of the tube and surrounding the outer circumference of the tube, the first projection having an outermost diameter not smaller than an inner diameter of the container. and a second projection provided on the tube, the second projection being configured to contact an end portion of the container facing the opening so as to prevent the tube from being inserted into the container by a depth not smaller than a predetermined depth or the capturing-retaining mechanism (104, 106, 204, 221) includes: a projection provided on an outer circumference of the tube; and a stopper provided on an inner wall of the container, the stopper being configured to contact the projection when the tube is inserted into the container. a container configured to store the sample therein; a tube configured to be inserted into the container; a filter part provided inside the tube, wherein, when the tube is inserted into the container, the filter part is configured to allow the stored sample to pass through the filter part so as to capture the plurality of solid components and to allow the liquid component to pass through the filter part; a capturing-retaining mechanism (104, 106, 204, 221) configured to prevent the plurality of captured solid components from being removed from the filter part when the sample passes through the filter part; and a cap provided at an opening end of the tube opposite to an opening end to which the filter part is joined and closing the opening end of the tube, the cap being configured to be removable from the opening end of the tube, wherein the cap is configured to hermetically seal the container to increase an inner pressure of the container when the tube is inserted into the container; wherein the container has an opening having the tube inserted therein, and wherein the capturing-retaining mechanism (104, 106, 204, 221) is structured such that: the capturing-retaining mechanism (104, 106, 204, 221) includes a first projection provided on an outer circumference of the tube and surrounding the outer circumference of the tube, the first projection having an outermost diameter not smaller than an inner diameter of the container. and a second projection provided on the tube, the second projection being configured to contact an end portion of the container facing the opening so as to prevent the tube from being inserted into the container by a depth not smaller than a predetermined depth or the capturing-retaining mechanism (104, 106, 204, 221) includes: a projection provided on an outer circumference of the tube; and a stopper provided on an inner wall of the container, the stopper being configured to contact the projection when the tube is inserted into the container. the capturing-retaining mechanism (104, 106, 204, 221) includes a first projection provided on an outer circumference of the tube and surrounding the outer circumference of the tube, the first projection having an outermost diameter not smaller than an inner diameter of the container. and a second projection provided on the tube, the second projection being configured to contact an end portion of the container facing the opening so as to prevent the tube from being inserted into the container by a depth not smaller than a predetermined depth or the capturing-retaining mechanism (104, 106, 204, 221) includes: a projection provided on an outer circumference of the tube; and a stopper provided on an inner wall of the container, the stopper being configured to contact the projection when the tube is inserted into the container. a projection provided on an outer circumference of the tube; and a stopper provided on an inner wall of the container, the stopper being configured to contact the projection when the tube is inserted into the container.