Depth filter

A depth filter, which is a cylindrical depth filter comprising a pre-filtration layer and a precision filtration layer disposed on a downstream side in a filtration direction of the pre-filtration layer,

• wherein the depth filter is formed by winding a mixed-fiber nonwoven fabric composed of a melt-blown fiber A made of a thermoplastic resin A and a melt-blown fiber B made of a thermoplastic resin B having a melting point lower than the thermoplastic resin A, and a single-fiber nonwoven fabric having an average fiber diameter of less than 1 μm and 0.1 μm or more, and a coefficient of variation of fiber diameter of 3.0 or less,
• the pre-filtration layer is a layer in which the mixed-fiber nonwoven fabric having an average fiber diameter of 20 μm or less and 1 μm or more is wound,
• the precision filtration layer is a layer in which the mixed-fiber nonwoven fabric having an average fiber diameter of less than 1 μm and 0.1 μm or more is wound,
• a gradient is provided in which an average fiber diameter of the mixed-fiber nonwoven fabric continuously decreases from the pre-filtration layer toward the precision filtration layer, and
• at least a part of the single-fiber nonwoven fabric is wound to overlap with a mixed-fiber nonwoven fabric constituting the precision filtration layer.