A separator includes a substrate layer that is porous, and a surface layer that is provided on at least one main face of the substrate layer and that has an uneven shape. The surface layer includes first particles that are for forming convexities of the uneven shape and that are a main component of the convexities, second particles that have a smaller average particle size than the first particles, cover at least a part of a surface of the first particles, and cover at least a part of a surface of the substrate layer that is exposed between the first particles, and a resin material.