A blood filter device includes: a housing that includes a dome 2 provided with a blood inlet, a filter retaining portion 3 that is positioned below the dome, and a bottom portion 4 provided with a blood outlet; and a filter 8 that is mounted in a cavity of the filter retaining portion and partitions a cavity of the housing into a dome side and a bottom portion side. A sheet-like filter member 8a of the filter forms a plurality of pleats, and ridgelines of the respective pleats traverse the filter retaining portion in parallel respectively. The blood filter device further includes an annular holder 9 intervening between the filter retaining portion and the filter, a annular rib substrate 10 that is disposed facing the ridgelines of the pleats in an outer peripheral region of the filter and has a plurality of ribs inserted respectively between the ridgelines of the plurality of pleats; and a bonding resin 11 that is charged into outer peripheral portions of the filter including the annular holder and the annular rib substrate, and bonds the outer peripheral portion of the filter to the filter retaining portion. Gaps are ensured between the plurality of pleats of the filter, and thus air bubbles can be removed easily.